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/l10n/gen/app_localizations_de.dart

@@ -1222,4 +1222,24 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get weekdayShortSunday => 'So';
+
+  @override
+  String stationCount(int count) {
+    String _temp0 = intl.Intl.pluralLogic(
+      count,
+      locale: localeName,
+      other: '$count Sender',
+      one: '1 Sender',
+    );
+    return '$_temp0';
+  }
+
+  @override
+  String get alarmIconLabel => 'Musikwecker';
+
+  @override
+  String get vacationIconLabel => 'Urlaubsmodus';
+
+  @override
+  String get streamUrlHint => 'https://stream.example.com:8000/radio';
 }