fix(devices): cache platform device names, dedupe placeholder ids, purge collided EQ entries

Dart half of bt-device-identity. EstadoEcualizador now caches each
device's platform-reported name in memory so the settings screen
shows the device's own Bluetooth name instead of its raw id when no
custom rename exists, and skips auto-creating preset entries for the
composite-placeholder sentinel. Enabling multi-device EQ triggers the
Bluetooth permission request through the new channel contract. A
flag-guarded one-time migration purges only entries keyed by the
exact literal placeholder id from the three per-device preference
maps, since those collided entries cannot be attributed to a device.

Work unit 2/2 of bt-device-identity (Dart state + migration).

lib/estado/estado_ecualizador.dart

@@ -26,6 +26,12 @@ import '../servicios/servicio_ecualizador.dart';
 /// When the toggle is false, resolution falls back to the original 2-level
 /// hierarchy (station → global) — zero behavioral change vs. prior releases.
 class EstadoEcualizador extends ChangeNotifier {
+  /// Composite-placeholder id prefix (bt-device-identity ADR-6): marks a
+  /// device whose real Bluetooth MAC is not yet known (BLUETOOTH_CONNECT
+  /// denied or unresolved). Devices with this prefix still update the
+  /// platform-name cache but never auto-create a `presetsDispositivo` entry.
+  static const _prefijoPlaceholderCompuesto = 'bt_a2dp:name:';
+
   EstadoEcualizador({
     required this.audio,
     ServicioEcualizador? servicio,
@@ -54,6 +60,13 @@ class EstadoEcualizador extends ChangeNotifier {
   /// Custom display names for devices: deviceId → custom name.
   final Map<String, String> _nombresDispositivos = {};
 
+  /// Last-seen platform (Bluetooth/productName) name per deviceId.
+  ///
+  /// In-memory only (bt-device-identity ADR-4) — NOT persisted. Devices
+  /// re-report their name on every enumeration, so this cache self-heals
+  /// every session without needing a SharedPreferences key or migration.
+  final Map<String, String> _nombresPlataforma = {};
+
   PresetEcualizador _presetPrincipal = PresetEcualizador.flat;
   PresetEcualizador _presetActual = PresetEcualizador.flat;
   bool _activo = true;
@@ -210,15 +223,27 @@ class EstadoEcualizador extends ChangeNotifier {
   Future<void> _onDispositivoCambiado(DispositivoAudio dispositivo) async {
     if (!_eqMultiDeviceEnabled) return;
 
+    // Cache updates on every event regardless of whether a preset entry
+    // gets created below (bt-device-identity ADR-4).
+    _nombresPlataforma[dispositivo.id] = dispositivo.nombre;
     _dispositivoActualId = dispositivo.id;
 
     // First-seen device: copy the current resolved preset as its starting
     // point. builtin_speaker is excluded: it must always fall through to
     // the hierarchy (L4 global) instead of being pinned by a forced L3
     // device-level copy, otherwise a later global-preset change would be
-    // masked by this stale entry for the base device.
+    // masked by this stale entry for the base device. Composite-placeholder
+    // ids are also excluded (bt-device-identity ADR-6): they are transient
+    // fallback ids for a device whose real MAC is not yet known, so
+    // persisting a preset entry for them would create dead noise that never
+    // resolves to the eventual real-MAC id.
     final esBase = dispositivo.tipo == TipoDispositivo.altavozInterno;
-    if (!esBase && !_presetsDispositivo.containsKey(dispositivo.id)) {
+    final esPlaceholderCompuesto = dispositivo.id.startsWith(
+      _prefijoPlaceholderCompuesto,
+    );
+    if (!esBase &&
+        !esPlaceholderCompuesto &&
+        !_presetsDispositivo.containsKey(dispositivo.id)) {
       final presetBase = _resolverPresetActivo();
       _presetsDispositivo[dispositivo.id] = presetBase;
       await servicio.guardarPresetDispositivo(dispositivo.id, presetBase);
@@ -252,6 +277,21 @@ class EstadoEcualizador extends ChangeNotifier {
     if (notificar) notifyListeners();
   }
 
+  /// Requests `BLUETOOTH_CONNECT` (API 31+) at the point the
+  /// device-management UI is opened (bt-device-identity ADR-1).
+  ///
+  /// Thin passthrough to the injected device service so callers don't need
+  /// [ServicioDispositivoAudio] wired as its own top-level `Provider` (Task
+  /// 4.8 — `ServicioDispositivoAudio` is only ever constructed inside
+  /// `EstadoRadio` today, not exposed via the provider tree; routing through
+  /// here avoids adding wiring the tree doesn't already have). Returns false
+  /// when no device service is injected.
+  Future<bool> solicitarPermisoBluetooth() async {
+    final svc = _dispositivoAudio;
+    if (svc == null) return false;
+    return svc.solicitarPermisoBluetooth();
+  }
+
   Future<void> cambiarPresetPrincipal(
     PresetEcualizador preset, {
     bool notificar = true,
@@ -353,6 +393,11 @@ class EstadoEcualizador extends ChangeNotifier {
   String obtenerNombreDispositivo(String deviceId) =>
       _nombresDispositivos[deviceId] ?? '';
 
+  /// Returns the last-seen platform name for [deviceId], or an empty string
+  /// if none has been observed yet (bt-device-identity ADR-4).
+  String nombrePlataforma(String deviceId) =>
+      _nombresPlataforma[deviceId] ?? '';
+
   /// Resolves the display name for [deviceId] using the fallback chain:
   /// custom name → [platformName] → raw [deviceId].
   String nombreVisible(String deviceId, String platformName) {