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/eslint.config.js

@@ -364,6 +364,14 @@ const HOVER_SWAP =
 const HOVER_SWAP_MESSAGE =
   "hover by a colour swap: use the B3 layer (`state-layer`, Pressable `layer`, `state-filled` on a fill), not hover:bg-card / bg-border / opacity-N.";
 
+// A palette colour (DESIGN.md Tokens "only semantic tokens", audit F16): nothing measures `text-amber-500`,
+// so a gold that reads on dark ships at 2:1 on light. Black and white are not matched: they are the
+// media scrims and the text on them, the same in every theme.
+const PALETTE =
+  "/(^|[\\s:])(text|bg|border|fill|stroke|from|via|to|ring|outline|decoration|divide|caret|shadow)-(red|orange|amber|yellow|lime|green|emerald|teal|cyan|sky|blue|indigo|violet|purple|fuchsia|pink|rose|slate|gray|zinc|neutral|stone)-\\d/";
+const PALETTE_MESSAGE =
+  "a palette colour: use a semantic token (text-rating, bg-live, bg-media-chrome, text-danger, …; DESIGN.md Tokens), not text-amber-500.";
+
 export default tseslint.config(
   { ignores: ["dist", "node_modules", "playwright-report", "test-results", "e2e/.auth"] },
   {
@@ -481,6 +489,8 @@ export default tseslint.config(
         { selector: `TemplateElement[value.raw=${Z_RAW}]`, message: Z_RAW_MESSAGE },
         { selector: `Literal[value=${HOVER_SWAP}]`, message: HOVER_SWAP_MESSAGE },
         { selector: `TemplateElement[value.raw=${HOVER_SWAP}]`, message: HOVER_SWAP_MESSAGE },
+        { selector: `Literal[value=${PALETTE}]`, message: PALETTE_MESSAGE },
+        { selector: `TemplateElement[value.raw=${PALETTE}]`, message: PALETTE_MESSAGE },
       ],
     },
   },