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/ui/Banner.tsx

@@ -2,20 +2,21 @@ import type { ReactNode } from "react";
 import { useTranslation } from "react-i18next";
 import type { LucideIcon } from "lucide-react";
 import { X } from "lucide-react";
+import { Button } from "./Button";
 import { IconButton } from "./IconButton";
 
 type BannerTone = "accent" | "warning";
 
-const TONES: Record<BannerTone, { bar: string; icon: string; action: string }> = {
+const TONES: Record<BannerTone, { bar: string; icon: string; action: "primary" | "warn" }> = {
   accent: {
     bar: "bg-accent/15 border-accent/30",
     icon: "text-accent",
-    action: "btn-primary",
+    action: "primary",
   },
   warning: {
     bar: "bg-warn/15 border-warn/30",
     icon: "text-warn",
-    action: "btn-warn",
+    action: "warn",
   },
 };
 
@@ -54,12 +55,14 @@ export default function Banner({
       <Icon className={`w-4 h-4 shrink-0 ${c.icon}`} />
       <span className="min-w-0">{children}</span>
       {action && (
-        <button
+        <Button
+          variant={c.action}
+          size="sm"
           onClick={action.onClick}
-          className={`ml-1 px-2.5 py-1 rounded-lg font-semibold transition ${c.action}`}
+          className="ml-1 font-semibold"
         >
           {action.label}
-        </button>
+        </Button>
       )}
       {onDismiss && (
         <IconButton
@@ -69,7 +72,7 @@ export default function Banner({
           onClick={onDismiss}
           className="ml-auto"
         >
-          <X className="w-4 h-4" />
+          <X />
         </IconButton>
       )}
     </div>