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/tema/pluri_animate.dart

@@ -33,6 +33,20 @@ extension PluriAnimate on Widget {
         .scaleXY(begin: begin, end: 1, duration: duration, curve: curve);
   }
 
+  /// Fade + subtle vertical slide entry animation.
+  Widget pluriFadeSlideIn(
+    BuildContext context, {
+    Duration duration = const Duration(milliseconds: 350),
+    Duration delay = Duration.zero,
+    Curve curve = Curves.easeOutCubic,
+    double beginY = 0.1,
+  }) {
+    if (_animacionesDeshabilitadas(context)) return this;
+    return animate(delay: delay)
+        .fadeIn(duration: duration, curve: curve)
+        .slideY(begin: beginY, end: 0, duration: duration, curve: curve);
+  }
+
   bool _animacionesDeshabilitadas(BuildContext context) =>
       MediaQuery.maybeDisableAnimationsOf(context) ?? false;
 }

lib/tema/pluriwave_tokens.dart

@@ -36,9 +36,19 @@ class PluriWaveTokens extends ThemeExtension<PluriWaveTokens> {
   final double spacingMd;
   final double spacingLg;
 
+  /// Brand accent (S5-R8). Same hue as [electricMagenta]; exposed as a
+  /// static const so const contexts (e.g. AudioServiceConfig) can use it.
+  static const Color brand = Color(0xFF21D4D9);
+
+  /// Secondary palette used by gradients and decorative orbs (S5-R1).
+  /// These are token DEFINITIONS — the only place raw literals may live.
+  static const Color brightCyan = Color(0xFF20E6FF);
+  static const Color auroraTeal = Color(0xFF0E4A4F);
+  static const Color skyBlue = Color(0xFF60A5FA);
+
   static const dark = PluriWaveTokens(
     deepViolet: Color(0xFF07121A),
-    electricMagenta: Color(0xFF21D4D9),
+    electricMagenta: brand,
     warmCoral: Color(0xFFF4B860),
     glassSurface: Color(0x1FFFFFFF),
     glassBorder: Color(0x33FFFFFF),
@@ -86,13 +96,19 @@ class PluriWaveTokens extends ThemeExtension<PluriWaveTokens> {
   }
 
   @override
-  PluriWaveTokens lerp(covariant ThemeExtension<PluriWaveTokens>? other, double t) {
+  PluriWaveTokens lerp(
+    covariant ThemeExtension<PluriWaveTokens>? other,
+    double t,
+  ) {
     if (other is! PluriWaveTokens) return this;
     return PluriWaveTokens(
       deepViolet: Color.lerp(deepViolet, other.deepViolet, t) ?? deepViolet,
-      electricMagenta: Color.lerp(electricMagenta, other.electricMagenta, t) ?? electricMagenta,
+      electricMagenta:
+          Color.lerp(electricMagenta, other.electricMagenta, t) ??
+          electricMagenta,
       warmCoral: Color.lerp(warmCoral, other.warmCoral, t) ?? warmCoral,
-      glassSurface: Color.lerp(glassSurface, other.glassSurface, t) ?? glassSurface,
+      glassSurface:
+          Color.lerp(glassSurface, other.glassSurface, t) ?? glassSurface,
       glassBorder: Color.lerp(glassBorder, other.glassBorder, t) ?? glassBorder,
       glowColor: Color.lerp(glowColor, other.glowColor, t) ?? glowColor,
       radiusSm: lerpDouble(radiusSm, other.radiusSm, t) ?? radiusSm,