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.dart

@@ -2245,6 +2245,30 @@ abstract class AppLocalizations {
   /// In es, this message translates to:
   /// **'Dom'**
   String get weekdayShortSunday;
+
+  /// No description provided for @stationCount.
+  ///
+  /// In es, this message translates to:
+  /// **'{count, plural, =1{1 emisora} other{{count} emisoras}}'**
+  String stationCount(int count);
+
+  /// No description provided for @alarmIconLabel.
+  ///
+  /// In es, this message translates to:
+  /// **'Alarma musical'**
+  String get alarmIconLabel;
+
+  /// No description provided for @vacationIconLabel.
+  ///
+  /// In es, this message translates to:
+  /// **'Modo vacaciones'**
+  String get vacationIconLabel;
+
+  /// No description provided for @streamUrlHint.
+  ///
+  /// In es, this message translates to:
+  /// **'https://stream.example.com:8000/radio'**
+  String get streamUrlHint;
 }
 
 class _AppLocalizationsDelegate