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).

test/servicios/servicio_ecualizador_test.dart

@@ -229,4 +229,181 @@ void main() {
       expect(restored.nombresDispositivos['bt_a2dp:AA:BB'], equals('My Speaker'));
     });
   });
+
+  // ---------------------------------------------------------------------------
+  // bt-device-identity Phase 5: one-time guarded migration purge
+  // ---------------------------------------------------------------------------
+
+  group('ServicioEcualizador — placeholder migration purge (bt-device-identity Phase 5)', () {
+    const placeholderKey = 'bt_a2dp:02:00:00:00:00:00';
+    const stableKey = 'bt_a2dp:AA:BB:CC:DD:EE:FF';
+
+    test(
+      '5.1 migration removes only exact placeholder entries from presetsPorDispositivo',
+      () async {
+        final prefs = await SharedPreferences.getInstance();
+        final servicio = ServicioEcualizador(prefs: prefs);
+        await servicio.guardarPresetDispositivo(
+          placeholderKey,
+          PresetEcualizador.jazz,
+        );
+        await servicio.guardarPresetDispositivo(
+          stableKey,
+          PresetEcualizador.rock,
+        );
+
+        await servicio.migrarClavesPlaceholder();
+        final config = await servicio.cargar();
+
+        expect(
+          config.presetsDispositivo.containsKey(placeholderKey),
+          isFalse,
+        );
+        expect(
+          config.presetsDispositivo[stableKey],
+          equals(PresetEcualizador.rock),
+        );
+      },
+    );
+
+    test('5.2 matrix keys purge only the placeholder segment', () async {
+      final prefs = await SharedPreferences.getInstance();
+      final servicio = ServicioEcualizador(prefs: prefs);
+      await servicio.guardarPresetMatriz(
+        'station1:$placeholderKey',
+        PresetEcualizador.jazz,
+      );
+      await servicio.guardarPresetMatriz(
+        'station1:$stableKey',
+        PresetEcualizador.rock,
+      );
+
+      await servicio.migrarClavesPlaceholder();
+      final config = await servicio.cargar();
+
+      expect(
+        config.presetsMatriz.containsKey('station1:$placeholderKey'),
+        isFalse,
+      );
+      expect(
+        config.presetsMatriz['station1:$stableKey'],
+        equals(PresetEcualizador.rock),
+      );
+    });
+
+    test('5.3 near-miss keys are preserved (differs by one digit)', () async {
+      const nearMissKey = 'bt_a2dp:02:00:00:00:00:01';
+      final prefs = await SharedPreferences.getInstance();
+      final servicio = ServicioEcualizador(prefs: prefs);
+      await servicio.guardarPresetDispositivo(
+        nearMissKey,
+        PresetEcualizador.jazz,
+      );
+
+      await servicio.migrarClavesPlaceholder();
+      final config = await servicio.cargar();
+
+      expect(
+        config.presetsDispositivo[nearMissKey],
+        equals(PresetEcualizador.jazz),
+      );
+    });
+
+    test('5.4 migration runs once (second run is a true no-op)', () async {
+      final prefs = await SharedPreferences.getInstance();
+      final servicio = ServicioEcualizador(prefs: prefs);
+      await servicio.guardarPresetDispositivo(
+        placeholderKey,
+        PresetEcualizador.jazz,
+      );
+      await servicio.guardarPresetDispositivo(
+        stableKey,
+        PresetEcualizador.rock,
+      );
+
+      await servicio.migrarClavesPlaceholder();
+
+      // Re-seed the placeholder key directly, bypassing the flag, to prove
+      // the SECOND migration call is a true no-op (flag short-circuits)
+      // rather than merely finding nothing left to purge.
+      await servicio.guardarPresetDispositivo(
+        placeholderKey,
+        PresetEcualizador.bassBoost,
+      );
+      await servicio.migrarClavesPlaceholder();
+
+      final config = await servicio.cargar();
+
+      expect(
+        config.presetsDispositivo[placeholderKey],
+        equals(PresetEcualizador.bassBoost),
+      );
+      expect(
+        config.presetsDispositivo[stableKey],
+        equals(PresetEcualizador.rock),
+      );
+    });
+
+    test(
+      '5.5 no placeholder entries when BLUETOOTH_CONNECT was never '
+      'requested is a no-op',
+      () async {
+        final prefs = await SharedPreferences.getInstance();
+        final servicio = ServicioEcualizador(prefs: prefs);
+        await servicio.guardarPresetDispositivo(
+          stableKey,
+          PresetEcualizador.rock,
+        );
+
+        await servicio.migrarClavesPlaceholder();
+        final config = await servicio.cargar();
+
+        expect(
+          config.presetsDispositivo[stableKey],
+          equals(PresetEcualizador.rock),
+        );
+        expect(config.presetsDispositivo.length, equals(1));
+      },
+    );
+
+    test('5.6 nombresDispositivos also purges the exact placeholder key', () async {
+      final prefs = await SharedPreferences.getInstance();
+      final servicio = ServicioEcualizador(prefs: prefs);
+      await servicio.guardarNombresDispositivos({
+        placeholderKey: 'Ghost Device',
+        stableKey: 'Living Room BT',
+      });
+
+      await servicio.migrarClavesPlaceholder();
+      final config = await servicio.cargar();
+
+      expect(config.nombresDispositivos.containsKey(placeholderKey), isFalse);
+      expect(
+        config.nombresDispositivos[stableKey],
+        equals('Living Room BT'),
+      );
+    });
+
+    test('5.9 cargar() runs the migration automatically on first load', () async {
+      final prefs = await SharedPreferences.getInstance();
+      final servicio = ServicioEcualizador(prefs: prefs);
+      await servicio.guardarPresetDispositivo(
+        placeholderKey,
+        PresetEcualizador.jazz,
+      );
+      await servicio.guardarPresetDispositivo(
+        stableKey,
+        PresetEcualizador.rock,
+      );
+
+      // No explicit migrarClavesPlaceholder() call: cargar() must run it.
+      final config = await servicio.cargar();
+
+      expect(config.presetsDispositivo.containsKey(placeholderKey), isFalse);
+      expect(
+        config.presetsDispositivo[stableKey],
+        equals(PresetEcualizador.rock),
+      );
+    });
+  });
 }