feat(panels): peek-open side panels with a docked tab

The shared SidePanel now follows the nav rail's model, so Filters, Plex and
Playlists all inherit it: unpinned it sits as a small tab docked flush against
the rail (replacing the full-height vertical strip) and expands into the card on
hover or keyboard focus without pushing content; pinned it stays expanded
in-flow. The collapse toggle became pin/unpin, and panels now default to
unpinned. The tab carries the active-filter count and an accent ring.

The tab stays mounted under the open card on purpose: swapping it out from under
the pointer drops the hover that opened the card, and unmounting it while
focused strands keyboard focus.

Measured: feed content starts at 123px instead of 336px when unpinned.

frontend/src/App.tsx

@@ -373,12 +373,13 @@ export default function App() {
   const [navCollapsed, setNavCollapsedState] = useState<boolean>(() =>
     Boolean(readAccount(LS.navCollapsed, true))
   );
+  // Default unpinned (tab + hover-expand overlay); accounts that explicitly pin keep their choice.
   const [filterCollapsed, setFilterCollapsedState] = useState<boolean>(() =>
-    Boolean(readAccount(LS.filterCollapsed, false))
+    Boolean(readAccount(LS.filterCollapsed, true))
   );
   // The Playlists rail has its own collapse flag (it's a list/navigator, not filters).
   const [playlistsCollapsed, setPlaylistsCollapsedState] = useState<boolean>(() =>
-    Boolean(readAccount(LS.playlistsCollapsed, false))
+    Boolean(readAccount(LS.playlistsCollapsed, true))
   );
   function setNavCollapsed(next: boolean) {
     setNavCollapsedState(next);

frontend/src/components/SidePanel.tsx

@@ -1,13 +1,14 @@
 import { type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
-import { Check, ChevronLeft, Pencil, RotateCcw } from "lucide-react";
+import { Check, Pencil, Pin, PinOff, RotateCcw } from "lucide-react";
 import { useScrollFade } from "../lib/useScrollFade";
+import { useHoverFocusWithin } from "../lib/useHoverFocusWithin";
 
-// The shared floating side panel — one shell for the Feed / Plex / Playlists rails so they read
-// as one system: a rounded glass card that floats beside the nav (aligned with the header top,
-// not reaching the page bottom), with a header (title + active count + Customize/Reset) and a
-// scrollable body whose native scrollbar is hidden and edges fade to hint more content. Collapses
-// to a slim vertical tab docked at the nav's right (it's the flex sibling right after the nav).
+// The shared floating side panel — one shell for the Feed / Plex / Playlists rails so they read as
+// one system, and the same peek-open model as the nav rail: unpinned it sits as a small tab docked
+// against the rail's right edge (this panel is the flex sibling right after it) and expands into a
+// rounded glass card on hover/focus WITHOUT pushing content; pinned it stays expanded in-flow.
+// `collapsed` (persisted per-account) therefore means "unpinned".
 export default function SidePanel({
   title,
   icon,
@@ -37,14 +38,29 @@ export default function SidePanel({
 }) {
   const { t } = useTranslation();
   const fade = useScrollFade();
+  const peek = useHoverFocusWithin();
+  const pinned = !collapsed;
+  const expanded = pinned || peek.active;
 
-  if (collapsed) {
-    return (
+  return (
+    // Layout slot: reserves only the tab's gutter when unpinned, so the expanded card overlays
+    // content instead of pushing it. Pinned reserves the full width (in-flow), as before.
+    <div
+      {...peek.handlers}
+      className={`hidden md:block relative shrink-0 transition-[width] ${
+        pinned ? "w-[268px]" : "w-9"
+      }`}
+    >
+      {/* The tab: a small handle flush against the nav rail, flat on the docked edge. It stays
+          mounted while the card is open (the card shares its top-left corner and covers it) —
+          swapping it out from under the pointer would drop the very hover that opened the card, and
+          unmounting it while focused would throw keyboard focus to nowhere. */}
       <button
         onClick={onToggleCollapse}
-        title={t("sidebar.expand")}
-        aria-label={t("sidebar.expand")}
-        className="hidden md:flex my-3 mr-3 w-11 shrink-0 rounded-2xl glass glass-hover flex-col items-center justify-center gap-3 text-fg"
+        aria-label={pinned ? t("sidebar.unpin") : t("sidebar.pin")}
+        className={`glass glass-hover absolute top-3 left-0 z-[34] flex flex-col items-center gap-2 px-1.5 py-3 rounded-l-none rounded-r-xl ${
+          count > 0 ? "ring-1 ring-accent/40" : ""
+        }`}
       >
         <span className="text-accent">{icon}</span>
         {count > 0 && (
@@ -59,69 +75,73 @@ export default function SidePanel({
           {title}
         </span>
       </button>
-    );
-  }
 
-  return (
-    <aside className="hidden md:flex my-3 mr-3 w-64 shrink-0 rounded-2xl glass flex-col overflow-hidden">
-      {/* Row 1 — identity only: collapse, icon, title (flexes + truncates last), count, customize.
-          Module actions live on their own row below so the title always has room. */}
-      <div className="flex items-center gap-1.5 px-3 py-2.5 border-b border-border/60 flex-none">
-        <button
-          onClick={onToggleCollapse}
-          title={t("sidebar.collapsePanel")}
-          aria-label={t("sidebar.collapsePanel")}
-          className="shrink-0 -ml-1 p-1 rounded-md text-muted hover:text-fg hover:bg-card transition"
-        >
-          <ChevronLeft className="w-4 h-4" />
-        </button>
-        <span className="shrink-0 flex text-accent">{icon}</span>
-        <span className="flex-1 min-w-0 truncate text-xs font-bold uppercase tracking-[0.12em]">
-          {title}
-        </span>
-        {count > 0 && (
-          <span
-            title={t("sidebar.activeCount", { count })}
-            className="shrink-0 min-w-[18px] h-[18px] px-1.5 rounded-full bg-accent/15 text-accent text-[11px] font-semibold inline-flex items-center justify-center tabular-nums"
-          >
-            {count}
-          </span>
-        )}
-        {editing && onReset && (
-          <button
-            onClick={onReset}
-            title={t("sidebar.resetDefaults")}
-            className="shrink-0 p-1.5 rounded-lg text-muted hover:text-fg hover:bg-card transition"
-          >
-            <RotateCcw className="w-4 h-4" />
-          </button>
-        )}
-        {onToggleEditing && (
-          <button
-            onClick={onToggleEditing}
-            title={editing ? t("sidebar.done") : t("sidebar.customize")}
-            className={`shrink-0 p-1.5 rounded-lg transition hover:bg-card ${
-              editing ? "text-accent" : "text-muted hover:text-fg"
-            }`}
-          >
-            {editing ? <Check className="w-4 h-4" /> : <Pencil className="w-4 h-4" />}
-          </button>
-        )}
-      </div>
+      {expanded && (
+        <aside className="glass absolute top-3 bottom-3 left-0 z-[35] w-64 rounded-2xl flex flex-col overflow-hidden">
+          {/* Row 1 — identity only: pin, icon, title (flexes + truncates last), count, customize.
+              Module actions live on their own row below so the title always has room. */}
+          <div className="flex items-center gap-1.5 px-3 py-2.5 border-b border-border/60 flex-none">
+            <button
+              onClick={onToggleCollapse}
+              title={pinned ? t("sidebar.unpin") : t("sidebar.pin")}
+              aria-label={pinned ? t("sidebar.unpin") : t("sidebar.pin")}
+              className="shrink-0 -ml-1 p-1 rounded-md text-muted hover:text-fg hover:bg-card transition"
+            >
+              {pinned ? <PinOff className="w-4 h-4" /> : <Pin className="w-4 h-4" />}
+            </button>
+            <span className="shrink-0 flex text-accent">{icon}</span>
+            <span className="flex-1 min-w-0 truncate text-xs font-bold uppercase tracking-[0.12em]">
+              {title}
+            </span>
+            {count > 0 && (
+              <span
+                title={t("sidebar.activeCount", { count })}
+                className="shrink-0 min-w-[18px] h-[18px] px-1.5 rounded-full bg-accent/15 text-accent text-[11px] font-semibold inline-flex items-center justify-center tabular-nums"
+              >
+                {count}
+              </span>
+            )}
+            {editing && onReset && (
+              <button
+                onClick={onReset}
+                title={t("sidebar.resetDefaults")}
+                className="shrink-0 p-1.5 rounded-lg text-muted hover:text-fg hover:bg-card transition"
+              >
+                <RotateCcw className="w-4 h-4" />
+              </button>
+            )}
+            {onToggleEditing && (
+              <button
+                onClick={onToggleEditing}
+                title={editing ? t("sidebar.done") : t("sidebar.customize")}
+                className={`shrink-0 p-1.5 rounded-lg transition hover:bg-card ${
+                  editing ? "text-accent" : "text-muted hover:text-fg"
+                }`}
+              >
+                {editing ? <Check className="w-4 h-4" /> : <Pencil className="w-4 h-4" />}
+              </button>
+            )}
+          </div>
 
-      {/* Row 2 — module actions (e.g. Clear all / Share), only when not customizing. */}
-      {!editing && actions && (
-        <div className="flex items-center justify-between gap-2 px-3 py-1.5 border-b border-border/60 flex-none">
-          {actions}
-        </div>
+          {/* Row 2 — module actions (e.g. Clear all / Share), only when not customizing. */}
+          {!editing && actions && (
+            <div className="flex items-center justify-between gap-2 px-3 py-1.5 border-b border-border/60 flex-none">
+              {actions}
+            </div>
+          )}
+
+          <div
+            ref={fade.ref}
+            style={fade.style}
+            className="flex-1 min-h-0 overflow-y-auto no-scrollbar"
+          >
+            <div className="p-3 space-y-3">
+              {editing && editHint && <div className="text-[11px] text-muted">{editHint}</div>}
+              {children}
+            </div>
+          </div>
+        </aside>
       )}
-
-      <div ref={fade.ref} style={fade.style} className="flex-1 min-h-0 overflow-y-auto no-scrollbar">
-        <div className="p-3 space-y-3">
-          {editing && editHint && <div className="text-[11px] text-muted">{editHint}</div>}
-          {children}
-        </div>
-      </div>
-    </aside>
+    </div>
   );
 }

frontend/src/i18n/locales/en/sidebar.json

@@ -16,8 +16,8 @@
   "hideWidget": "Hide widget",
   "expand": "Expand",
   "collapse": "Collapse",
-  "collapsePanel": "Collapse filters",
-  "expandPanel": "Expand filters",
+  "pin": "Pin panel open",
+  "unpin": "Unpin panel",
   "any": "Any",
   "all": "All",
   "tagModeTooltip": "Match any vs all selected tags",

frontend/src/i18n/locales/hu/sidebar.json

@@ -16,8 +16,8 @@
   "hideWidget": "Modul elrejtése",
   "expand": "Kibontás",
   "collapse": "Összecsukás",
-  "collapsePanel": "Szűrők összecsukása",
-  "expandPanel": "Szűrők kibontása",
+  "pin": "Panel rögzítése nyitva",
+  "unpin": "Panel rögzítésének feloldása",
   "any": "Bármelyik",
   "all": "Összes",
   "tagModeTooltip": "Bármelyik vagy az összes kijelölt címke illeszkedjen",