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/app.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 import 'estado/estado_radio.dart';
 import 'estado/estado_alarmas.dart';
 import 'estado/estado_idioma.dart';
@@ -23,15 +24,21 @@ import 'package:pluriwave/widgets/mini_reproductor.dart';
 import 'servicios/servicio_alarmas_android.dart';
 
 class PluriWaveApp extends StatelessWidget {
-  const PluriWaveApp({super.key});
+  const PluriWaveApp({super.key, this.prefs});
+
+  /// Single SharedPreferences instance resolved in main() (S3-R4) and
+  /// injected into every state/service.
+  final SharedPreferences? prefs;
 
   @override
   Widget build(BuildContext context) {
     return MultiProvider(
       providers: [
-        ChangeNotifierProvider(create: (_) => EstadoRadio()),
-        ChangeNotifierProvider(create: (_) => EstadoAlarmas()),
-        ChangeNotifierProvider(create: (_) => EstadoIdioma()),
+        ChangeNotifierProvider(create: (_) => EstadoRadio(prefs: prefs)),
+        ChangeNotifierProvider(create: (_) => EstadoAlarmas(prefs: prefs)),
+        ChangeNotifierProvider(
+          create: (_) => EstadoIdioma(sharedPreferences: prefs),
+        ),
       ],
       child: Consumer<EstadoIdioma>(
         builder:
@@ -69,6 +76,7 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
   bool _alarmaSonandoActiva = false;
   bool _onboardingInicialSolicitado = false;
   String? _alarmaSonandoId;
+  Locale? _localeAlarmasConfigurado;
 
   static const _paginas = [
     PantallaInicio(),
@@ -89,6 +97,15 @@ class _PaginaPrincipalState extends State<_PaginaPrincipal> {
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
+    // S3-R3 / Decision 3.2: keep the alarm bridge l10n in sync, once per
+    // locale change (this hook re-runs when Localizations changes).
+    final locale = Localizations.localeOf(context);
+    if (_localeAlarmasConfigurado != locale) {
+      _localeAlarmasConfigurado = locale;
+      context.read<EstadoAlarmas>().configurarLocalizaciones(
+        AppLocalizations.of(context),
+      );
+    }
     final estado = context.read<EstadoRadio>();
     if (identical(_estadoSuscrito, estado) && _errorSubscription != null) {
       return;