fix(design): rating and live colour tokens, the player's menus over its notices, the info overlay on a light theme (E28)

- F16: --rating (theme-scoped gold, 4.5:1 on the page and its chip), --rating-media, --live/--live-fg,
  --media-chrome replace 14 palette literals; a lint rule refuses palette classes; the theme contract
  measures them.
- The Plex player's notices drew over its open settings/tracks popovers: notices z-base, popovers z-menu.
- The player's info overlay rendered theme tokens on its always-dark panel: on a light theme the score
  (2.6:1), collection years (3.2:1) and cast initials (1.05:1) were unreadable; onDark variants now.
- The lint-rule contract tests share one ESLint with a one-off warm-up (a cold first lint took 8 s,
  past vitest's 5 s).

frontend/src/design-lab/batchC.tsx

@@ -108,7 +108,7 @@ function C3() {
       title="The players on touch"
       rule="Plex: a tap on the video only shows or hides the controls; play/pause is the button (the mouse keeps click-to-pause). The hide timer starts with playback, not with the first touch. The seek track stays thin inside a 44px hit area with touch-action: none, its head always visible. Buttons 44. The YouTube modal's chrome uses the Button rungs (44 on touch), its side arrows stay inside the screen, and its description opens from an ⓘ button, because the hover popover never opens on a tap."
     >
-      <div className="relative aspect-video overflow-hidden rounded-xl bg-linear-to-br from-slate-700 to-black text-white">
+      <div className="relative aspect-video overflow-hidden rounded-xl bg-linear-to-br from-white/25 to-black text-white">
         <div className="absolute inset-x-0 bottom-0 flex flex-col gap-1 bg-linear-to-t from-black/80 to-transparent px-3 pb-2 pt-8">
           {/* The visible track stays thin; the dashed box is the 44-tall hit area around it. */}
           <div
@@ -233,7 +233,7 @@ const ctl = "grid h-11 w-11 shrink-0 place-items-center rounded-full";
 
 function PlayerRow() {
   return (
-    <div className="relative aspect-4/3 w-full overflow-hidden rounded-xl bg-linear-to-br from-slate-700 to-black text-white">
+    <div className="relative aspect-4/3 w-full overflow-hidden rounded-xl bg-linear-to-br from-white/25 to-black text-white">
       {/* Double-tap zones: the left and right thirds of the picture skip ∓10 s on touch. */}
       <div className="absolute inset-x-0 top-0 bottom-28 flex justify-between text-2xs text-white/70">
         <span className="flex w-1/3 items-start justify-center border-r border-dashed border-white/25 pt-6">