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/widgets/visualizador_audio.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
 import '../servicios/servicio_audio.dart';
+import '../tema/pluriwave_tokens.dart';
 
 /// Visualizador de audio para el reproductor.
 ///
@@ -234,7 +235,9 @@ class _WaveFlowPainter extends CustomPainter {
             colors: [
               color.withValues(alpha: 0.08),
               color.withValues(alpha: active ? 0.95 : 0.35),
-              const Color(0xFFF4B860).withValues(alpha: active ? 0.75 : 0.20),
+              PluriWaveTokens.dark.warmCoral.withValues(
+                alpha: active ? 0.75 : 0.20,
+              ),
               color.withValues(alpha: 0.08),
             ],
           ).createShader(Offset.zero & size);