fix(android): PlayerController transport methods dispatch to controller thread

After DIDL fix, Sonos accepted SetAVTransportURI + Play, but
playerController.pause() threw IllegalStateException 'method is
called from a wrong thread' because selectUpnp runs the whole
UPnP-selection flow on Dispatchers.Default. UI tap handlers were
fine - they're already on Main - but the cross-thread background
call from OutputPickerController.selectUpnp hit the MediaController's
application-thread guard.

Same fix as the cold-boot resume one earlier today (commit e69a5204
wrapped setQueue): pause / play / seekTo / skipToNext / skipToPrevious
now route through runOnControllerThread, which is a no-op when
already on the application looper and Handler.post otherwise.

Logcat from on-device confirmed Sonos plays after this fix lands -
SetAVTransportURI -> 200, Play -> 200, then the IllegalStateException
was the last failure path.

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

@@ -130,11 +130,24 @@ class PlayerController @Inject constructor(
 
     // ── Transport (no-op until the controller is connected) ──────────────
 
-    fun play() { mediaController?.play() }
-    fun pause() { mediaController?.pause() }
-    fun seekTo(positionMs: Long) { mediaController?.seekTo(positionMs) }
-    fun skipToNext() { mediaController?.seekToNextMediaItem() }
-    fun skipToPrevious() { mediaController?.seekToPreviousMediaItem() }
+    // Each transport call must run on the MediaController's
+    // applicationLooper; calling from a background coroutine throws
+    // IllegalStateException (see PlayerController.setQueue's note).
+    // UI tap handlers are already on Main so the in-place branch hits;
+    // the background path only fires for cross-thread callers like
+    // OutputPickerController.selectUpnp (which calls pause() after
+    // handing playback off to a UPnP renderer).
+    fun play() { mediaController?.let { runOnControllerThread(it) { it.play() } } }
+    fun pause() { mediaController?.let { runOnControllerThread(it) { it.pause() } } }
+    fun seekTo(positionMs: Long) {
+        mediaController?.let { runOnControllerThread(it) { it.seekTo(positionMs) } }
+    }
+    fun skipToNext() {
+        mediaController?.let { runOnControllerThread(it) { it.seekToNextMediaItem() } }
+    }
+    fun skipToPrevious() {
+        mediaController?.let { runOnControllerThread(it) { it.seekToPreviousMediaItem() } }
+    }
 
     /** Flip shuffle on/off. Media3 emits onEvents → uiState reflects. */
     fun toggleShuffle() {