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/WatchPage.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useId, useRef, useState } from "react";
 import { Download, File as FileIcon, Link2, Lock, PlayCircle, Repeat } from "lucide-react";
 import { Button } from "./ui/Button";
+import { Chip } from "./ui/Chip";
 import { formatBytes } from "../lib/format";
 import { exposeVideoToBackgroundPlay } from "../lib/browserBackgroundPlay";
 import { LS, readJSON, writeJSON } from "../lib/storage";
@@ -385,14 +386,15 @@ export default function WatchPage() {
               <div className="flex shrink-0 items-center gap-2">
                 {/* An on/off toggle, so the shared pressed-pill paint (a solid fill when on) — not a
                     Button, whose variants differ only in colour. */}
-                <button
-                  type="button"
-                  aria-pressed={repeat}
+                <Chip
+                  size="md"
+                  pressed={repeat}
+                  icon={<Repeat className="size-3.5" aria-hidden />}
                   onClick={toggleRepeat}
-                  className="pill inline-flex items-center gap-1.5 rounded-lg border px-3 py-2 text-sm font-medium"
+                  className="font-medium"
                 >
-                  <Repeat className="w-4 h-4" aria-hidden /> {T.repeat}
-                </button>
+                  {T.repeat}
+                </Chip>
                 {meta.allow_download && (
                   <a
                     href={meta.file_url}