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/l10n/gen/app_localizations_ar.dart

@@ -1225,4 +1225,26 @@ class AppLocalizationsAr extends AppLocalizations {
 
   @override
   String get streamUrlHint => 'https://stream.example.com:8000/radio';
+
+  @override
+  String get advancedEqSectionTitle => 'Opciones avanzadas de ecualización';
+
+  @override
+  String get advancedEqEnableToggle => 'Activar EQ por dispositivo';
+
+  @override
+  String get advancedEqEnableToggleSubtitle =>
+      'Aplica automáticamente un preset de EQ distinto al cambiar la salida de audio.';
+
+  @override
+  String get advancedEqKnownDevicesTitle => 'Dispositivos de audio conocidos';
+
+  @override
+  String get advancedEqKnownDevicesEmpty =>
+      'No hay dispositivos registrados. Conectá uno para empezar.';
+
+  @override
+  String advancedEqDevicePresetLabel(Object presetName) {
+    return 'Preset: $presetName';
+  }
 }