feat: refresh views on all playlist mutations

- Add EV_PLAYLIST_TRACK_ADDED (22) — emitted when a track is
  successfully added to a playlist
- If the currently-open playlist is the one modified, re-fetch it
  so the track appears in the list immediately
- After creating a playlist, open it automatically so the user
  lands in the new (empty) playlist view right away
- Sidebar already refreshes on create/delete; this ensures the
  track list view also stays in sync

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rust/include/qobuz_backend.h

@@ -31,8 +31,9 @@ enum QobuzEvent {
     EV_TRACK_URL_OK   = 17,
     EV_TRACK_URL_ERR  = 18,
     EV_GENERIC_ERR      = 19,
-    EV_PLAYLIST_CREATED = 20,
-    EV_PLAYLIST_DELETED = 21,
+    EV_PLAYLIST_CREATED      = 20,
+    EV_PLAYLIST_DELETED      = 21,
+    EV_PLAYLIST_TRACK_ADDED  = 22,
 };
 
 // Callback signature