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/DownloadDialog.tsx

@@ -77,13 +77,9 @@ export default function DownloadDialog({
         onChange={([v]) => v && setProfileId(Number(v))}
         options={profiles.map((p) => ({ value: String(p.id), label: p.name }))}
       />
-      <button
-        type="button"
-        onClick={() => setManage(true)}
-        className="text-xs text-accent hover:underline mt-1 mb-4"
-      >
+      <Button variant="link" onClick={() => setManage(true)} className="text-xs mt-1 mb-4">
         {t("downloads.dialog.manage")}
-      </button>
+      </Button>
 
       <label className="block text-sm font-medium mb-1">{t("downloads.dialog.nameLabel")}</label>
       <input