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

test/helpers/fakes.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:pluriwave/l10n/gen/app_localizations.dart';
 import 'package:pluriwave/modelos/emisora.dart';
 import 'package:pluriwave/modelos/grupo_favoritos.dart';
 import 'package:pluriwave/modelos/preset_ecualizador.dart';
@@ -20,9 +21,16 @@ class FakeServicioAudio extends ServicioAudio {
   final List<bool> cambiosEcualizadorActivo = [];
   final List<double> volumenesAplicados = [];
   int pausas = 0;
+  int configuracionesL10n = 0;
   Emisora? _emisoraActual;
   EstadoReproduccion _estadoActual = EstadoReproduccion.detenido;
 
+  @override
+  void configurarLocalizaciones(AppLocalizations l10n) {
+    // No global handler in tests; just record the call.
+    configuracionesL10n++;
+  }
+
   @override
   Emisora? get emisoraActual => _emisoraActual;