feat(player): download works in fullscreen + de-dup the transport controls (R8 S5)

Two R8 S5 (player big-view control-bar) follow-ups:

- Modal now portals into `document.fullscreenElement ?? document.body` (reactive), the
  same fullscreen-aware root the popover platform uses. A node under <body> is painted
  beneath whatever holds the fullscreen lock, so the download dialog — a Modal, opened
  from the player's control bar — would open invisibly in true fullscreen. With that
  fixed, the `!isFullscreen` guard on the player's DownloadButton is dropped, so download
  joins add-to-playlist as working in true fullscreen. (Every Modal is now fullscreen-
  aware; the fix is at the primitive, not the call site.)

- The queue transport cluster (prev / counter / next + auto-advance + loop toggles) was
  duplicated inline in two places — the modal queue bar and the big-view docked control
  bar — with identical logic and only theme + label-visibility differing. Extracted a
  `<PlayerTransportControls variant="modal"|"docked">`; a mode/icon change now lands once.
  Behaviour-preserving (the docked bar's trailing divider and the wrapper rows stay at the
  call sites). Note the modal variant keeps its `bg-accent/15` active tint, which is a
  latent no-op under Tailwind v3's hex --accent — left as-is for R10 S0's styling audit.

Gate green (tsc/eslint/76 vitest). Device-UAT'd in real Chrome: transport controls render
correctly in both the modal queue bar and the docked bar; the download button now shows in
true fullscreen and its dialog portals into the fullscreen stage, fully visible and
centered. No console errors.

frontend/src/components/Modal.tsx

@@ -4,11 +4,14 @@ import { useTranslation } from "react-i18next";
 import { X } from "lucide-react";
 import { useBackToClose } from "../lib/history";
 import { pushLayer, removeLayer, isTopmost } from "../lib/layerStack";
+import { useFullscreenElement } from "../lib/fullscreen";
 
-// Small centered modal shell (portaled to <body>): backdrop + ESC + scroll-lock close. Each open
-// modal is a layer in the shared `layerStack` so ESC only closes the topmost one — e.g. an error
-// dialog over the tag editor dismisses just the error and returns to the editor underneath, and a
-// player below defers to it (R8 S3).
+// Small centered modal shell: backdrop + ESC + scroll-lock close. Each open modal is a layer in the
+// shared `layerStack` so ESC only closes the topmost one — e.g. an error dialog over the tag editor
+// dismisses just the error and returns to the editor underneath, and a player below defers to it
+// (R8 S3). Portals into `document.fullscreenElement ?? document.body`: a node under <body> is painted
+// beneath whatever holds the fullscreen lock, so a Modal opened from a player in true fullscreen (the
+// download dialog) would otherwise open invisibly.
 export default function Modal({
   title,
   onClose,
@@ -23,6 +26,7 @@ export default function Modal({
   const { t } = useTranslation();
   // Browser/mouse Back closes the topmost modal instead of navigating away.
   useBackToClose(onClose);
+  const fsRoot = useFullscreenElement();
 
   // Backdrop-click close must only fire when the press STARTED on the backdrop too. Otherwise a
   // drag that begins inside the dialog (e.g. selecting text in an input) and is released out on
@@ -79,6 +83,6 @@ export default function Modal({
         <div className="px-5 pb-5">{children}</div>
       </div>
     </div>,
-    document.body,
+    fsRoot ?? document.body,
   );
 }

frontend/src/components/PlayerModal.tsx

@@ -68,6 +68,108 @@ type LoopMode = "off" | "one" | "all";
 const AUTO_MODES: AutoMode[] = ["off", "next", "prev", "random"];
 const LOOP_MODES: LoopMode[] = ["off", "one", "all"];
 
+/** The queue transport cluster — prev / counter / next, then the auto-advance and loop mode toggles.
+ *  Rendered in two places with identical logic: the modal's queue bar (`variant:"modal"`, normal glass
+ *  theme, labels always shown) and the big-view docked control bar (`variant:"docked"`, white-on-dark,
+ *  labels hidden until a breakpoint). Only the theme + label-visibility differ; the behaviour is one,
+ *  so a mode/icon change lands once. The wrapper (fragment vs. bordered row) stays at the call site. */
+function PlayerTransportControls({
+  variant,
+  index,
+  queueLength,
+  autoMode,
+  loopMode,
+  onPrev,
+  onNext,
+  onCycleAuto,
+  onCycleLoop,
+}: {
+  variant: "docked" | "modal";
+  index: number;
+  queueLength: number;
+  autoMode: AutoMode;
+  loopMode: LoopMode;
+  onPrev: () => void;
+  onNext: () => void;
+  onCycleAuto: () => void;
+  onCycleLoop: () => void;
+}) {
+  const { t } = useTranslation();
+  const docked = variant === "docked";
+  const navBtn = docked
+    ? "inline-flex items-center gap-1 text-white/80 enabled:hover:text-white disabled:opacity-30 transition"
+    : "inline-flex items-center gap-1.5 text-muted enabled:hover:text-fg disabled:opacity-40 transition";
+  const navLabel = docked ? "hidden sm:inline" : "";
+  const counter = docked ? "tabular-nums text-white/70" : "text-muted tabular-nums";
+  const divider = docked ? "h-4 w-px bg-white/20" : "w-px h-4 bg-border";
+  const toggle = (on: boolean) =>
+    docked
+      ? `inline-flex items-center gap-1 rounded-lg px-2 py-1 transition ${
+          on ? "bg-white/20 text-white" : "text-white/70 hover:bg-white/10 hover:text-white"
+        }`
+      : `inline-flex items-center gap-1.5 rounded-lg px-2.5 py-1 transition ${
+          on ? "bg-accent/15 text-accent" : "text-muted hover:bg-surface hover:text-fg"
+        }`;
+  const toggleLabel = docked ? "hidden md:inline" : "";
+  return (
+    <>
+      <button
+        onClick={onPrev}
+        disabled={index === 0}
+        title={`${t("player.previous")} · Shift+←`}
+        className={navBtn}
+      >
+        <SkipBack className="h-4 w-4" />
+        <span className={navLabel}>{t("player.previous")}</span>
+      </button>
+      <span className={counter}>
+        {index + 1} / {queueLength}
+      </span>
+      <button
+        onClick={onNext}
+        disabled={index === queueLength - 1}
+        title={`${t("player.next")} · Shift+→`}
+        className={navBtn}
+      >
+        <span className={navLabel}>{t("player.next")}</span>
+        <SkipForward className="h-4 w-4" />
+      </button>
+      <span className={divider} />
+      {/* Persistent playback settings — cycle on click, saved to your account. */}
+      <button
+        onClick={onCycleAuto}
+        title={t("player.autoAdvance.hint")}
+        className={toggle(autoMode !== "off")}
+      >
+        {autoMode === "prev" ? (
+          <SkipBack className="h-3.5 w-3.5" />
+        ) : autoMode === "random" ? (
+          <Shuffle className="h-3.5 w-3.5" />
+        ) : (
+          <SkipForward className="h-3.5 w-3.5" />
+        )}
+        <span className={toggleLabel}>
+          {t("player.autoAdvance.label")}: {t(`player.autoAdvance.${autoMode}`)}
+        </span>
+      </button>
+      <button
+        onClick={onCycleLoop}
+        title={t("player.loop.hint")}
+        className={toggle(loopMode !== "off")}
+      >
+        {loopMode === "one" ? (
+          <Repeat1 className="h-3.5 w-3.5" />
+        ) : (
+          <Repeat className="h-3.5 w-3.5" />
+        )}
+        <span className={toggleLabel}>
+          {t("player.loop.label")}: {t(`player.loop.${loopMode}`)}
+        </span>
+      </button>
+    </>
+  );
+}
+
 /** Can `el` (or an ancestor inside the modal) still scroll vertically in `dir` (-1 up, 1 down)?
  * Used to leave ArrowUp/ArrowDown alone while there is content to scroll — the volume shortcut
  * must not eat the only keyboard way to read a long description. Stops at `<body>`: the page
@@ -877,82 +979,30 @@ export default function PlayerModal({
               >
                 {hasQueue && (
                   <>
-                    <button
-                      onClick={goPrev}
-                      disabled={index === 0}
-                      title={`${t("player.previous")} · Shift+←`}
-                      className="inline-flex items-center gap-1 text-white/80 enabled:hover:text-white disabled:opacity-30 transition"
-                    >
-                      <SkipBack className="h-4 w-4" />
-                      <span className="hidden sm:inline">{t("player.previous")}</span>
-                    </button>
-                    <span className="tabular-nums text-white/70">
-                      {index + 1} / {queue!.length}
-                    </span>
-                    <button
-                      onClick={goNext}
-                      disabled={index === queue!.length - 1}
-                      title={`${t("player.next")} · Shift+→`}
-                      className="inline-flex items-center gap-1 text-white/80 enabled:hover:text-white disabled:opacity-30 transition"
-                    >
-                      <span className="hidden sm:inline">{t("player.next")}</span>
-                      <SkipForward className="h-4 w-4" />
-                    </button>
-                    <span className="h-4 w-px bg-white/20" />
-                    <button
-                      onClick={cycleAuto}
-                      title={t("player.autoAdvance.hint")}
-                      className={`inline-flex items-center gap-1 rounded-lg px-2 py-1 transition ${
-                        autoMode !== "off"
-                          ? "bg-white/20 text-white"
-                          : "text-white/70 hover:bg-white/10 hover:text-white"
-                      }`}
-                    >
-                      {autoMode === "prev" ? (
-                        <SkipBack className="h-3.5 w-3.5" />
-                      ) : autoMode === "random" ? (
-                        <Shuffle className="h-3.5 w-3.5" />
-                      ) : (
-                        <SkipForward className="h-3.5 w-3.5" />
-                      )}
-                      <span className="hidden md:inline">
-                        {t("player.autoAdvance.label")}: {t(`player.autoAdvance.${autoMode}`)}
-                      </span>
-                    </button>
-                    <button
-                      onClick={cycleLoop}
-                      title={t("player.loop.hint")}
-                      className={`inline-flex items-center gap-1 rounded-lg px-2 py-1 transition ${
-                        loopMode !== "off"
-                          ? "bg-white/20 text-white"
-                          : "text-white/70 hover:bg-white/10 hover:text-white"
-                      }`}
-                    >
-                      {loopMode === "one" ? (
-                        <Repeat1 className="h-3.5 w-3.5" />
-                      ) : (
-                        <Repeat className="h-3.5 w-3.5" />
-                      )}
-                      <span className="hidden md:inline">
-                        {t("player.loop.label")}: {t(`player.loop.${loopMode}`)}
-                      </span>
-                    </button>
+                    <PlayerTransportControls
+                      variant="docked"
+                      index={index}
+                      queueLength={queue!.length}
+                      autoMode={autoMode}
+                      loopMode={loopMode}
+                      onPrev={goPrev}
+                      onNext={goNext}
+                      onCycleAuto={cycleAuto}
+                      onCycleLoop={cycleLoop}
+                    />
                     <span className="h-4 w-px bg-white/20" />
                   </>
                 )}
-                {/* Works in fullscreen now: its menu rides the popover platform, which portals into
-                    the fullscreen element instead of <body> (a body-portaled node is painted
-                    underneath the element holding the lock, i.e. invisible). */}
+                {/* Both work in fullscreen now: add-to-playlist's popover and download's Modal both
+                    portal into the fullscreen element rather than <body> (a body-portaled node is
+                    painted underneath the element holding the lock, i.e. invisible). */}
                 {!navigated && (
                   <AddToPlaylist
                     videoId={active.id}
                     className="inline-flex h-8 w-8 items-center justify-center rounded-lg text-white/80 hover:bg-white/10 hover:text-white transition"
                   />
                 )}
-                {/* Still hidden in fullscreen: this one opens a Modal, not a popover, and Modal
-                    still portals to <body> — so the dialog would open invisibly. Lifting that needs
-                    the same fullscreen-aware root in Modal. */}
-                {!navigated && !isFullscreen && (
+                {!navigated && (
                   <DownloadButton
                     videoId={active.id}
                     title={active.title}
@@ -1050,61 +1100,17 @@ export default function PlayerModal({
 
           {hasQueue && (
             <div className="flex flex-wrap items-center justify-center gap-x-4 gap-y-1.5 px-4 py-2 border-b border-border text-sm">
-              <button
-                onClick={goPrev}
-                disabled={index === 0}
-                title={`${t("player.previous")} · Shift+←`}
-                className="inline-flex items-center gap-1.5 text-muted enabled:hover:text-fg disabled:opacity-40 transition"
-              >
-                <SkipBack className="w-4 h-4" /> {t("player.previous")}
-              </button>
-              <span className="text-muted tabular-nums">
-                {index + 1} / {queue!.length}
-              </span>
-              <button
-                onClick={goNext}
-                disabled={index === queue!.length - 1}
-                title={`${t("player.next")} · Shift+→`}
-                className="inline-flex items-center gap-1.5 text-muted enabled:hover:text-fg disabled:opacity-40 transition"
-              >
-                {t("player.next")} <SkipForward className="w-4 h-4" />
-              </button>
-              <span className="w-px h-4 bg-border" />
-              {/* Persistent playback settings — cycle on click, saved to your account. */}
-              <button
-                onClick={cycleAuto}
-                title={t("player.autoAdvance.hint")}
-                className={`inline-flex items-center gap-1.5 rounded-lg px-2.5 py-1 transition ${
-                  autoMode !== "off"
-                    ? "bg-accent/15 text-accent"
-                    : "text-muted hover:bg-surface hover:text-fg"
-                }`}
-              >
-                {autoMode === "prev" ? (
-                  <SkipBack className="h-3.5 w-3.5" />
-                ) : autoMode === "random" ? (
-                  <Shuffle className="h-3.5 w-3.5" />
-                ) : (
-                  <SkipForward className="h-3.5 w-3.5" />
-                )}
-                {t("player.autoAdvance.label")}: {t(`player.autoAdvance.${autoMode}`)}
-              </button>
-              <button
-                onClick={cycleLoop}
-                title={t("player.loop.hint")}
-                className={`inline-flex items-center gap-1.5 rounded-lg px-2.5 py-1 transition ${
-                  loopMode !== "off"
-                    ? "bg-accent/15 text-accent"
-                    : "text-muted hover:bg-surface hover:text-fg"
-                }`}
-              >
-                {loopMode === "one" ? (
-                  <Repeat1 className="h-3.5 w-3.5" />
-                ) : (
-                  <Repeat className="h-3.5 w-3.5" />
-                )}
-                {t("player.loop.label")}: {t(`player.loop.${loopMode}`)}
-              </button>
+              <PlayerTransportControls
+                variant="modal"
+                index={index}
+                queueLength={queue!.length}
+                autoMode={autoMode}
+                loopMode={loopMode}
+                onPrev={goPrev}
+                onNext={goNext}
+                onCycleAuto={cycleAuto}
+                onCycleLoop={cycleLoop}
+              />
             </div>
           )}