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/index.css

@@ -40,6 +40,11 @@
   --color-warn-fg: var(--warn-fg);
   --color-success: var(--success);
   --color-success-fg: var(--success-fg);
+  --color-rating: var(--rating);
+  --color-rating-media: var(--rating-media);
+  --color-live: var(--live);
+  --color-live-fg: var(--live-fg);
+  --color-media-chrome: var(--media-chrome);
 
   --font-sans: Inter, system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
 
@@ -988,6 +993,7 @@ html[data-theme="dark"] {
   --success-fg: #052016;
   --info: #60a5fa;
   --info-fg: #08172e;
+  --rating: #fbbf24;
 }
 html[data-theme="light"] {
   /* red-700, like warn (amber-700) and success (emerald-700): red-600 fell to 4.43:1 on the tinted
@@ -1000,6 +1006,19 @@ html[data-theme="light"] {
   --success-fg: #ffffff;
   --info: #2563eb;
   --info-fg: #ffffff;
+  --rating: #854d0e; /* yellow-800: yellow-700 fell to 3.7:1 on its own 15% chip */
+}
+
+/* ===== Media colours (F16) =====
+   Theme-INDEPENDENT: they sit on a picture (a thumbnail, a poster's scrim, the player), and the
+   picture does not change with the theme. `--rating` above is the page's copy of the rating gold, so it
+   is theme-scoped like a status; it is not a status (a score is not a warning), hence its own token.
+   theme.contract.test.ts measures all of them. */
+:root {
+  --live: #dc2626; /* a broadcast's red, under --live-fg; ≥ 3:1 as a glyph on every page */
+  --live-fg: #ffffff;
+  --rating-media: #fcd34d; /* a score on a poster's black scrim */
+  --media-chrome: #171717; /* the always-dark player's menus and bars, under white text */
 }
 
 /* Toast auto-dismiss countdown bar (shrinks left-to-right to zero) */