feat(audio): audio session integration and runtime robustness

- Integrate audio_session (new servicio_audio_session.dart): incoming calls pause the radio and resume on end, headphone unplug pauses without auto-resume, permanent focus loss never auto-resumes, duck lowers volume
- Add play-intent flag to ServicioAudio so interruption handling and future reconnect logic can distinguish user pause from system-driven stops
- Eliminate read-modify-write race in ServicioAlarmas with an in-memory cache and single-writer queue across all mutations; recalcularTodas persists only when state actually changed
- Convert ServicioAlarmasAndroid static StreamController/handler to injectable instance fields, restoring test isolation
- Inject a single cached SharedPreferences from main.dart across services and state (removes 23 inline getInstance() calls)
- Move configurarLocalizaciones out of MiniReproductor.build() (was running on every rebuild during playback)
- Bound the alarm fire-dedup set (cap 200 entries, 24h pruning)
- 12 new tests (89 total green), flutter analyze clean

lib/widgets/mini_reproductor.dart

@@ -13,14 +13,34 @@ import 'visualizador_audio.dart';
 
 /// Barra inferior persistente con controles básicos de reproducción.
 /// Toca la barra para abrir PantallaReproductor completa.
-class MiniReproductor extends StatelessWidget {
+class MiniReproductor extends StatefulWidget {
   const MiniReproductor({super.key});
 
+  @override
+  State<MiniReproductor> createState() => _MiniReproductorState();
+}
+
+class _MiniReproductorState extends State<MiniReproductor> {
+  Locale? _localeConfigurado;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    // S3-R3: configure localizations once per locale change — never from
+    // build(), which re-runs on every playback notification.
+    final locale = Localizations.localeOf(context);
+    if (_localeConfigurado != locale) {
+      _localeConfigurado = locale;
+      context.read<EstadoRadio>().configurarLocalizaciones(
+        AppLocalizations.of(context),
+      );
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     final estado = context.watch<EstadoRadio>();
     final l10n = AppLocalizations.of(context);
-    estado.configurarLocalizaciones(l10n);
     final emisora = estado.emisoraActual;
 
     if (emisora == null) return const SizedBox.shrink();