feat(eq): add per-device equalizer with 4-level preset resolution

Introduce multi-device EQ support allowing each audio output device
(built-in speaker, wired, USB, individual Bluetooth by MAC) to have
its own equalizer preset, combined with existing per-station presets
for a full station×device matrix.

- Add DispositivoAudio model and ServicioDispositivoAudio interface
- Add Android platform channel (AudioDeviceCallback) for device detection
- Add iOS AudioDevicesPlugin (AVAudioSession route tracking)
- Extend ServicioEcualizador with device and matrix persistence keys
- Implement 4-level resolution: matrix > station > device > global
- Add advanced EQ settings section with feature toggle (off by default)
- Extend export/import to v3 with backward compatibility
- 184 tests passing, zero analyzer issues

lib/app.dart

@@ -25,6 +25,7 @@ import 'widgets/pluri_onboarding_dialog.dart';
 import 'widgets/pluri_wave_scaffold.dart';
 import 'package:pluriwave/widgets/mini_reproductor.dart';
 import 'servicios/servicio_alarmas_android.dart';
+import 'servicios/servicio_dispositivo_audio.dart';
 
 class PluriWaveApp extends StatelessWidget {
   const PluriWaveApp({super.key, this.prefs});
@@ -37,7 +38,13 @@ class PluriWaveApp extends StatelessWidget {
   Widget build(BuildContext context) {
     return MultiProvider(
       providers: [
-        ChangeNotifierProvider(create: (_) => EstadoRadio(prefs: prefs)),
+        ChangeNotifierProvider(
+          create:
+              (_) => EstadoRadio(
+                prefs: prefs,
+                dispositivoAudio: ServicioDispositivoAudioReal(),
+              ),
+        ),
         // Domain notifiers (S4-R1/R2/R3). Created and disposed by EstadoRadio
         // (they need its services and callbacks at construction); these
         // providers only expose the instances, so they declare no dispose