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/PlexDiscover.tsx

@@ -14,6 +14,7 @@ import { PlexPinMenu } from "./ComfortPinMenu";
 import { useContextMenu } from "./ui/useContextMenu";
 import { LoadingState, StateMessage } from "./ui/QueryState";
 import NavGrid from "./ui/NavGrid";
+import { IconButton } from "./ui/IconButton";
 
 // The Plex "Discover" landing (E5 S4): a stack of horizontal Carousel rails served from ONE
 // /api/plex/discover call — Continue watching, Recently added, Browse by genre (tiles), Because you
@@ -213,15 +214,13 @@ export default function PlexDiscover({
           ariaLabel={t("plex.discover.surprise")}
           cards={surprise}
           action={
-            <button
-              type="button"
+            <IconButton
               onClick={() => surpriseQ.refetch()}
-              aria-label={t("plex.discover.reshuffle")}
-              title={t("plex.discover.reshuffle")}
-              className="rounded-full p-1 text-muted transition hover:text-accent"
+              loading={surpriseQ.isFetching}
+              label={t("plex.discover.reshuffle")}
             >
-              <RotateCcw className={`h-3.5 w-3.5 ${surpriseQ.isFetching ? "animate-spin" : ""}`} />
-            </button>
+              <RotateCcw />
+            </IconButton>
           }
           {...railProps}
         />