feat(android): MinstrelPlayerService — Media3 MediaSessionService (M8 phase 6.2)

The actual replacement for everything audio_service plugin wrapped.
Media3 owns the foreground-service lifecycle, MediaSession token,
notification card, lock-screen surface, Bluetooth/AVRCP routing,
Pixel Watch tile, and Android Auto adapter natively — no plugin
layer between us and the platform.

Service shape (~25 LOC):
  - @AndroidEntryPoint MediaSessionService
  - @Inject PlayerFactory builds ExoPlayer in onCreate
  - onGetSession returns the live MediaSession to any binding
    controller (system UI, Wear OS companion, MediaController3 clients)
  - onTaskRemoved keeps playing while audio is active (standard
    media-app behavior); otherwise stopSelf so notification clears
  - onDestroy releases session + player

Compare with flutter_client/lib/player/audio_handler.dart's 1000+ LOC
across MinstrelAudioHandler + the soft-teardown / stall-watchdog /
recovery machinery. Media3 owns most of that natively; we'll get to
the small portions we still need (queue management, position
reporting facade) in 6.3.

Manifest registration: foregroundServiceType="mediaPlayback" +
MediaSessionService intent-filter. MediaButtonReceiver is registered
by the Media3 library; no manual receiver class needed (Flutter's
manifest had to declare audio_service's receiver explicitly).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -31,6 +31,13 @@
             </intent-filter>
         </activity>
 
-        <!-- Media3 MediaSessionService is registered in Phase 6 (Task 6.2). -->
+        <service
+            android:name=".player.MinstrelPlayerService"
+            android:exported="true"
+            android:foregroundServiceType="mediaPlayback">
+            <intent-filter>
+                <action android:name="androidx.media3.session.MediaSessionService" />
+            </intent-filter>
+        </service>
     </application>
 </manifest>

android/app/src/main/java/com/fabledsword/minstrel/player/MinstrelPlayerService.kt

@@ -0,0 +1,64 @@
+package com.fabledsword.minstrel.player
+
+import android.content.Intent
+import androidx.media3.common.Player
+import androidx.media3.session.MediaSession
+import androidx.media3.session.MediaSessionService
+import dagger.hilt.android.AndroidEntryPoint
+import javax.inject.Inject
+
+/**
+ * The app's foreground media-playback service. Replaces what the Flutter
+ * audio_service plugin wrapped — Media3 owns the foreground lifecycle,
+ * the MediaSession, the notification card, lock-screen surface, BT/AVRCP
+ * routing, Pixel Watch tile, and Android Auto adapter natively.
+ *
+ * Manifest declares this with `foregroundServiceType="mediaPlayback"`
+ * plus the standard `MediaSessionService` intent-filter — Media3's
+ * MediaButtonReceiver is registered automatically by the library, no
+ * manual receiver class needed.
+ *
+ * Lifecycle:
+ *   - onCreate: build the ExoPlayer + MediaSession once.
+ *   - onGetSession: return the live session to any binding controller
+ *     (system UI media card, Wear OS companion, MediaController3 clients).
+ *   - onTaskRemoved: if the user swipes the app away, keep playing when
+ *     audio is active (standard media-app behavior — music shouldn't
+ *     die because the app left recents); otherwise stop the service so
+ *     the lingering notification clears.
+ *   - onDestroy: release the session + player.
+ */
+@AndroidEntryPoint
+class MinstrelPlayerService : MediaSessionService() {
+
+    @Inject lateinit var playerFactory: PlayerFactory
+
+    private var mediaSession: MediaSession? = null
+
+    override fun onCreate() {
+        super.onCreate()
+        val player = playerFactory.build()
+        mediaSession = MediaSession.Builder(this, player).build()
+    }
+
+    override fun onGetSession(controllerInfo: MediaSession.ControllerInfo): MediaSession? =
+        mediaSession
+
+    override fun onTaskRemoved(rootIntent: Intent?) {
+        val player = mediaSession?.player ?: return super.onTaskRemoved(rootIntent)
+        val activelyPlaying = player.playWhenReady && player.playbackState != Player.STATE_ENDED
+        if (!activelyPlaying) {
+            stopSelf()
+        }
+        super.onTaskRemoved(rootIntent)
+    }
+
+    override fun onDestroy() {
+        mediaSession?.run {
+            player.release()
+            release()
+        }
+        mediaSession = null
+        super.onDestroy()
+    }
+}