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/ChannelStatsPopover.tsx

@@ -14,6 +14,7 @@ import { type MyStatus } from "../lib/api";
 import { formatEta, formatNumber } from "../lib/format";
 import { PopoverSurface } from "./ui/AnchoredPopover";
 import { useAnchoredPopover } from "./ui/anchoredPopoverHooks";
+import { Button } from "./ui/Button";
 
 // The channel-manager catalog stats, collapsed from a crowded inline row into a compact "Stats" chip
 // that reveals the numbers on hover (reuses the AnchoredPopover hover mode). One row per stat, each
@@ -77,15 +78,15 @@ export default function ChannelStatsPopover({ status }: { status: MyStatus }) {
 
   return (
     <>
-      <button
-        type="button"
+      <Button
+        variant="glass"
+        size="sm"
+        icon={<BarChart3 aria-hidden="true" />}
         ref={pop.refs.setReference}
         {...pop.getReferenceProps()}
-        className="glass-card glass-hover inline-flex items-center gap-1.5 rounded-lg px-2.5 py-1.5 text-sm text-muted transition"
       >
-        <BarChart3 className="h-4 w-4" aria-hidden="true" />
         {t("channels.stats.label")}
-      </button>
+      </Button>
       <PopoverSurface
         popover={pop}
         ariaLabel={t("channels.stats.label")}