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/Playlists.tsx

@@ -550,7 +550,7 @@ export default function Playlists() {
     return (
       <div className="text-sm p-4 flex flex-col items-start gap-3">
         <span className="inline-flex items-center gap-2 text-muted">
-          <AlertTriangle className="w-4 h-4 text-red-400" />
+          <AlertTriangle className="w-4 h-4 text-danger" />
           {t("playlists.loadFailed")}
         </span>
         <button
@@ -673,7 +673,7 @@ export default function Playlists() {
                     onClick={deletePlaylist}
                     title={t("playlists.delete")}
                     aria-label={t("playlists.delete")}
-                    className="inline-flex items-center justify-center p-2 rounded-lg border border-border text-muted hover:text-red-400 hover:border-red-400/50 transition"
+                    className="inline-flex items-center justify-center p-2 rounded-lg border border-border text-muted hover:text-danger hover:border-danger/50 transition"
                   >
                     <Trash2 className="w-3.5 h-3.5" />
                   </button>