Pause music playback when another app takes audio focus (#1842)

## Description
The audio player passed handleAudioFocus = false when setting its audio
attributes, so ExoPlayer never requested audio focus. Music kept playing
and mixed with other audio when a call arrived, another app started
playback, or voice search took focus.

### Related issues
Fixes https://github.com/damontecres/Wholphin/issues/1841

### Testing
1. Play a music track
2. Open YouTube and play a video

## AI or LLM usage
Cursor and Claude Code

app/src/main/java/com/github/damontecres/wholphin/services/PlayerFactory.kt

@@ -202,9 +202,10 @@ class PlayerFactory
                     it.setAudioAttributes(
                         AudioAttributes
                             .Builder()
+                            .setUsage(C.USAGE_MEDIA)
                             .setContentType(C.AUDIO_CONTENT_TYPE_MUSIC)
                             .build(),
-                        false,
+                        true,
                     )
                 }
         }