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/pantallas/pantalla_buscar.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/material.dart';
-import 'package:flutter_animate/flutter_animate.dart';
 import 'package:provider/provider.dart';
 
 import '../estado/estado_busqueda.dart';
+import '../tema/pluri_animate.dart';
 import '../l10n/gen/app_localizations.dart';
 import '../widgets/pluri_glass_surface.dart';
 import '../widgets/pluri_icon.dart';
@@ -260,9 +260,18 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
   Widget _resultados(EstadoBusqueda estado, ThemeData theme) {
     final l10n = AppLocalizations.of(context);
     if (estado.cargando) {
-      return const SizedBox(
-        height: 220,
-        child: Center(child: CircularProgressIndicator()),
+      // S5-R6: shimmer placeholders instead of a bare spinner, consistent
+      // with the loading pattern used by the home grid.
+      return Padding(
+        padding: const EdgeInsets.all(PluriLayout.horizontal),
+        child: Column(
+          children: [
+            for (var i = 0; i < 4; i++) ...[
+              const TarjetaEmisoraShimmer(esCompacta: true),
+              if (i < 3) const SizedBox(height: 10),
+            ],
+          ],
+        ),
       );
     }
 
@@ -310,7 +319,11 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
           emisora: resultados[i],
           esCompacta: true,
           onTap: () => reproducirMinimizado(context, resultados[i]),
-        ).animate().fadeIn(delay: (i.clamp(0, 12) * 20).ms).slideY(begin: 0.08);
+        ).pluriFadeSlideIn(
+          context,
+          delay: Duration(milliseconds: i.clamp(0, 12) * 20),
+          beginY: 0.08,
+        );
       },
     );
   }