feat(theme): R10 S1 — semantic status colors (danger/warn/success)

Add theme-scoped --danger/--warn/--success (+ -fg) tokens wired into the v4
@theme inline, replacing ~110 raw red/amber/emerald/green palette refs across
34 files. Fixes light-theme contrast failures (fixed Tailwind shades fell to
~1.7-3:1 on white). Status colors are scheme-independent — recognised by hue,
shifting only by theme to hold contrast (bright on dark bg, darkened on light).
Solid fills use the paired -fg text; @source inline guarantees the full -fg set
exists. IMDb rating gold kept as a deliberate decorative non-status exception.

frontend/src/components/ChannelPage.tsx

@@ -325,7 +325,7 @@ export default function ChannelPage({
                 ) : (
                   ch?.explored &&
                   !ch?.subscribed && (
-                    <span className="text-xs px-2 py-0.5 rounded-full bg-amber-500/15 text-amber-600 dark:text-amber-400">
+                    <span className="text-xs px-2 py-0.5 rounded-full bg-warn/15 text-warn dark:text-warn">
                       {t("channel.exploringBadge")}
                     </span>
                   )