feat(ui): design token discipline, accessibility and i18n pass

- Replace all hardcoded Color literals outside lib/tema with theme tokens (new static brand palette in PluriWaveTokens); media notification uses the brand color instead of the Material default purple
- Favorite button on station cards grows to a 48dp target and becomes an independent semantics node for screen readers (Semantics container fix)
- All flutter_animate call sites route through the PluriAnimate reduced-motion gate (zero direct .animate() left)
- Locale-aware short dates via intl DateFormat (new lib/l10n/formato_fechas.dart) replacing the hardcoded DD/MM/YYYY; proper plural messages for the favorites counter; example stream URL as a localized key - all 13 locales
- Rounded shimmer placeholders matching card radii; shimmer loading state in search instead of a bare spinner; rounded icon variants unified in settings; bottom-sheet conventions on the custom station form
- Fix latent debug crash: vacation editor read AppLocalizations in initState
- 11 new tests (121 total green), flutter analyze clean

lib/main.dart

@@ -8,9 +8,20 @@ import 'package:shared_preferences/shared_preferences.dart';
 import 'app.dart';
 import 'servicios/servicio_audio.dart';
 import 'servicios/servicio_audio_session.dart';
+import 'tema/pluriwave_tokens.dart';
 
 const _anchoMinimoLandscape = 600.0;
 
+/// S5-R8: media notification accent uses the brand color, not the M3
+/// default purple. Top-level const so tests can assert it.
+const configuracionAudioService = AudioServiceConfig(
+  androidNotificationChannelId: 'es.freetimelab.pluriwave.audio',
+  androidNotificationChannelName: 'PluriWave Radio',
+  androidNotificationOngoing: true,
+  androidStopForegroundOnPause: true,
+  notificationColor: PluriWaveTokens.brand,
+);
+
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
   await _aplicarPoliticaOrientacion();
@@ -21,13 +32,7 @@ Future<void> main() async {
 
   final handler = await AudioService.init(
     builder: () => PluriWaveAudioHandler(),
-    config: const AudioServiceConfig(
-      androidNotificationChannelId: 'es.freetimelab.pluriwave.audio',
-      androidNotificationChannelName: 'PluriWave Radio',
-      androidNotificationOngoing: true,
-      androidStopForegroundOnPause: true,
-      notificationColor: Color(0xFF6750A4),
-    ),
+    config: configuracionAudioService,
   );
   registrarHandler(handler);