feat(design): every button on its family, the chip primitive, the lint rule (E28 S3b2)

The second half of the button sweep: the remaining hand-rolled buttons in
feature components, the design lab and the components/ui composites now
stand on Button, IconButton, Pressable, Chip or DragHandle.

- Chip + DismissibleChip (filter / token / tag / suggest / ghost, 24px
  floor, 44 on touch) replace five chip geometries; FilterChipGroup
  renders Chips; overflow lanes measure a mirror painted by chipClass.
- The Plex control row is IconButton's player rung (36, 20px glyph,
  round, overlay; 44 on touch); the YT modal bar is on the sm rung with
  pressed cycle toggles and names that survive a folded label.
- New variants: IconButton ghost-accent, danger-soft; Button warn on a
  new state-warn utility. The .btn-{tone} recipes and btnCls are gone.
- Fixed on the way: membership rows (collection editor, Plex playlist
  add) announce checked/mixed; a one-letter tag chip was 21px wide;
  descriptionLinks moved out of lib/ (it renders components).
- local/button-primitive: a raw <button>/<FocusSafeButton> outside the
  control-primitive files is a lint error (contract-tested, seen red).

frontend/src/components/PaletteLauncher.tsx

@@ -2,6 +2,7 @@ import { useTranslation } from "react-i18next";
 import { Command } from "lucide-react";
 
 import { SHORTCUTS, formatChord, openPalette } from "../lib/keymap";
+import { Pressable } from "./ui/Pressable";
 
 // The visible way into the command palette (and, from there, the shortcut sheet). Ctrl/Cmd+K and
 // `h` had no entry point anywhere but a palette row — the one in-app pointer to the cheat sheet sat
@@ -30,15 +31,14 @@ export function PaletteKeycap() {
   const { t } = useTranslation();
   const cap = useCap();
   return (
-    <button
-      type="button"
+    <Pressable
       onClick={openPalette}
       aria-label={`${t("palette.open")} (${cap})`}
       title={`${t("palette.open")} (${cap})`}
       className="shrink-0 rounded-md border border-border px-1.5 py-0.5 font-mono text-3xs text-muted transition hover:border-accent/50 hover:text-fg @max-[640px]/appmain:hidden"
     >
       {cap}
-    </button>
+    </Pressable>
   );
 }
 
@@ -47,8 +47,7 @@ export function PaletteLauncher() {
   const { t } = useTranslation();
   const cap = useCap();
   return (
-    <button
-      type="button"
+    <Pressable
       onClick={openPalette}
       title={t("palette.open")}
       className="pointer-events-auto glass-menu flex h-11 items-center gap-2 rounded-2xl px-3 text-sm text-muted transition hover:text-fg"
@@ -58,6 +57,6 @@ export function PaletteLauncher() {
       <span className="rounded-md border border-border px-1.5 py-0.5 font-mono text-3xs @max-[640px]/appmain:hidden">
         {cap}
       </span>
-    </button>
+    </Pressable>
   );
 }