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/backgroundDisplay.h

@@ -22,6 +22,8 @@
 #include <string>
 #include <atomic>
 
+#include "timeline.h"
+
 namespace bd {
 
 struct TermSize {
@@ -62,15 +64,21 @@ struct PlayVideoOptions {
     bool loop = false;              // repeat the video until stop
     float intensity = 1.0f;         // brightness multiplier for fg/bg
     bool tryResize = true;          // false => force the "not adjustable" fit path
-    int bottomRows = 0;             // leave this many rows at the bottom for other content
+    int topRows = 0;                // reserve this many rows ABOVE the video (e.g. lyrics)
+    int bottomRows = 0;             // reserve this many rows BELOW the video
+    GridSize* outGrid = nullptr;    // receives the computed video grid (optional)
+    int* outOffsetX = nullptr;      // receives the video's horizontal offset in cols
+    std::atomic<bool>* gridReady = nullptr;  // set true once the layout is reported
     std::atomic<bool>* stop = nullptr;  // set to true to end playback early
 };
 
-// Play `path` as ASCII art. Blocks until the video ends (or `stop` is set).
+// Play `path` as ASCII art, paced by `timeline` (may be null for an
+// independent local clock). Blocks until the video ends (or `stop` is set).
 // Returns:
 //   0  playback finished (or stopped) cleanly
 //   1  failed to open/decode the video
 //   2  stdout is not a tty (nothing was written)
-int playVideo(const std::string& path, const PlayVideoOptions& opts = {});
+int playVideo(const std::string& path, Timeline* timeline,
+              const PlayVideoOptions& opts = {});
 
 }  // namespace bd