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/pantallas/pantalla_ajustes.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:io';
 
 import 'package:file_picker/file_picker.dart';
@@ -698,7 +699,8 @@ class _SeccionEcualizadorAvanzado extends StatelessWidget {
                   child: GestureDetector(
                     behavior: HitTestBehavior.translucent,
                     onTap:
-                        () => eq.cambiarMultiDeviceEnabled(!multiDeviceEnabled),
+                        () =>
+                            _alternarMultiDevice(eq, !multiDeviceEnabled),
                     child: Column(
                       crossAxisAlignment: CrossAxisAlignment.start,
                       children: [
@@ -718,7 +720,7 @@ class _SeccionEcualizadorAvanzado extends StatelessWidget {
                 Switch.adaptive(
                   value: multiDeviceEnabled,
                   onChanged:
-                      (habilitado) => eq.cambiarMultiDeviceEnabled(habilitado),
+                      (habilitado) => _alternarMultiDevice(eq, habilitado),
                 ),
               ],
             ),
@@ -749,6 +751,17 @@ class _SeccionEcualizadorAvanzado extends StatelessWidget {
       ),
     );
   }
+
+  /// Toggles the multi-device EQ feature and, when turning it ON, requests
+  /// `BLUETOOTH_CONNECT` at this point-of-intent (bt-device-identity ADR-1)
+  /// so BT devices report their real MAC instead of the OS placeholder.
+  /// Fire-and-forget: neither call blocks the toggle UI on its result.
+  void _alternarMultiDevice(EstadoEcualizador eq, bool habilitado) {
+    unawaited(eq.cambiarMultiDeviceEnabled(habilitado));
+    if (habilitado) {
+      unawaited(eq.solicitarPermisoBluetooth());
+    }
+  }
 }
 
 /// A single device row in the known-devices list.
@@ -766,7 +779,7 @@ class _FilaDispositivo extends StatelessWidget {
     final l10n = AppLocalizations.of(context);
     final eq = context.watch<EstadoEcualizador>();
     final isActive = eq.dispositivoActualId == deviceId;
-    final displayName = eq.nombreVisible(deviceId, '');
+    final displayName = eq.nombreVisible(deviceId, eq.nombrePlataforma(deviceId));
 
     return Padding(
       padding: const EdgeInsets.symmetric(vertical: 6),
@@ -843,7 +856,10 @@ class _DialogoEdicionDispositivoState
   void initState() {
     super.initState();
     final eq = context.read<EstadoEcualizador>();
-    final displayName = eq.nombreVisible(widget.deviceId, '');
+    final displayName = eq.nombreVisible(
+      widget.deviceId,
+      eq.nombrePlataforma(widget.deviceId),
+    );
     _nombreCtrl = TextEditingController(text: displayName);
     _presetActual = widget.preset;
   }