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/components/plexCards.tsx

@@ -100,7 +100,7 @@ export function PlexPosterCard({
               <span
                 role="img"
                 aria-label={t(`plex.playable.${cls}`)}
-                className={`absolute top-1.5 left-1.5 z-menu w-2 h-2 rounded-full ring-2 ring-black/40 ${PLAYABLE_TINT[cls] ?? "bg-gray-400"}`}
+                className={`absolute top-1.5 left-1.5 z-menu w-2 h-2 rounded-full ring-2 ring-black/40 ${PLAYABLE_TINT[cls] ?? "bg-muted"}`}
                 title={t(`plex.playable.${cls}`)}
               />
             );
@@ -164,7 +164,7 @@ export function PlexPosterCard({
                   <span>{[card.year, runtime].filter(Boolean).join(" · ")}</span>
                 )}
                 {card.rating != null && (
-                  <span className="inline-flex items-center gap-0.5 text-amber-300">
+                  <span className="inline-flex items-center gap-0.5 text-rating-media">
                     <Star className="w-3 h-3 fill-current" />
                     {card.rating.toFixed(1)}
                   </span>