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.

tools/demo.cpp

@@ -10,6 +10,7 @@
 #include "backgroundDisplay.h"
 #include "lyricResolve.h"
 #include "musicPlayer.h"
+#include "timeline.h"
 
 #include <atomic>
 #include <chrono>
@@ -42,8 +43,9 @@ static void usage(const char* argv0) {
         argv0, HMS_DEMO_VIDEO, HMS_DEMO_MUSIC, HMS_DEMO_LYRICS);
 }
 
-static void playMusicQuietly(const std::string& path, std::atomic<bool>* stop) {
-    const int rc = mp::play(path, stop);
+static void playMusicQuietly(const std::string& path, Timeline* timeline,
+                             std::atomic<bool>* stop) {
+    const int rc = mp::play(path, timeline, stop);
     if (rc == 2) {
         std::fprintf(stderr, "demo: cannot open audio file '%s'\n", path.c_str());
     } else if (rc == 3) {
@@ -86,6 +88,8 @@ int main(int argc, char** argv) {
     }
 
     std::atomic<bool> stop{false};
+    Timeline timeline;
+    timeline.start();
 
     // Optional hard deadline (e.g. for quick verification).
     std::thread deadlineThread;
@@ -99,8 +103,8 @@ int main(int argc, char** argv) {
     if (!useVideo) {
         // No video: just music + lyrics.
         std::thread musicThread, lyricThread;
-        if (useMusic) musicThread = std::thread([&] { playMusicQuietly(music, &stop); });
-        if (useLyrics) lyricThread = std::thread([&] { lr::playLyricsFile(lyrics, {}, &stop); });
+        if (useMusic) musicThread = std::thread([&] { playMusicQuietly(music, &timeline, &stop); });
+        if (useLyrics) lyricThread = std::thread([&] { lr::playLyricsFile(lyrics, {}, &timeline, &stop); });
         if (musicThread.joinable()) musicThread.join();
         if (lyricThread.joinable()) lyricThread.join();
     } else if (!useMusic && !useLyrics) {
@@ -110,7 +114,7 @@ int main(int argc, char** argv) {
         vo.loop = false;
         vo.tryResize = tryResize;
         vo.stop = &stop;
-        bd::playVideo(video, vo);
+        bd::playVideo(video, &timeline, vo);
     } else {
         // Full show: video loops in the background, music + lyrics on top.
         // Reserve the bottom row for the lyric line.
@@ -121,7 +125,7 @@ int main(int argc, char** argv) {
             vo.tryResize = tryResize;
             vo.bottomRows = useLyrics ? 1 : 0;
             vo.stop = &stop;
-            bd::playVideo(video, vo);
+            bd::playVideo(video, &timeline, vo);
         });
 
         // Give the video a moment to detect and adjust the terminal size so
@@ -129,8 +133,8 @@ int main(int argc, char** argv) {
         std::this_thread::sleep_for(std::chrono::milliseconds(400));
 
         std::thread musicThread, lyricThread;
-        if (useMusic) musicThread = std::thread([&] { playMusicQuietly(music, &stop); });
-        if (useLyrics) lyricThread = std::thread([&] { lr::playLyricsFile(lyrics, {}, &stop); });
+        if (useMusic) musicThread = std::thread([&] { playMusicQuietly(music, &timeline, &stop); });
+        if (useLyrics) lyricThread = std::thread([&] { lr::playLyricsFile(lyrics, {}, &timeline, &stop); });
         if (musicThread.joinable()) musicThread.join();
         if (lyricThread.joinable()) lyricThread.join();