feat: make everything threads-safe.

feat: complete `uninstall.sh` logic to make everything synced.
	feat: complete basic play logic to handle background, music,
	lyric play.

modules/musicPlayer.h

@@ -10,13 +10,18 @@
 #include <atomic>
 #include <string>
 
+#include "timeline.h"
+
 namespace mp {
 
-// Blocking playback of `path`. Returns 0 on success (played to the end or
-// stopped early via `stop`). Non-zero return values:
+// Blocking playback of `path` in real time. `timeline` is optional; if given
+// and not yet anchored, the music anchors it (audio is the show's clock).
+// Returns 0 on success (played to the end or stopped early via `stop`).
+// Non-zero return values:
 //   1  argument error
 //   2  could not open/decode the file
 //   3  no audio device available (caller should degrade gracefully)
-int play(const std::string& path, std::atomic<bool>* stop = nullptr);
+int play(const std::string& path, Timeline* timeline = nullptr,
+         std::atomic<bool>* stop = nullptr);
 
 }  // namespace mp