Merge main (auto-save played videos, lyrics editor audio) into beta

frontend/app.js

@@ -657,6 +657,7 @@ const DEFAULT_SETTINGS = {
   quality: 'auto', volume: 1, audioOnly: false, autoPreload: true,
   p2pShare: true,           // P2P (docs/p2p-architecture.md): share my saved videos with other devices — ON by default
   p2pReceive: true,         // fetch from other devices when YouTube and the server can't — ON by default
+  autoSavePlayed: true,     // keep every video you play for offline (background save once playback starts)
   saveBeforePlay: false,    // download (server-muxed single file) before playing instead of streaming
   repeatMode: 'off',        // 'off' | 'all' — repeat the playing list when it ends
   loopOne: false,           // repeat the single current video
@@ -1999,6 +2000,20 @@ function markCardCacheState(id, state) {
   });
 }
 
+// Auto-save what you play: once a video starts playing, save it in the
+// background (never delays playback). One attempt per video per page session.
+const autoSaveTried = new Set();
+document.addEventListener('play', () => {
+  const m = current && current.meta;
+  if (!m || !m.id || m.custom || current.localUrl) return;
+  if (data.settings.autoSavePlayed === false) return;
+  if (!WEB) return;
+  if (cachedIds.has(m.id) || downloading.has(m.id) || autoSaveTried.has(m.id)) return;
+  autoSaveTried.add(m.id);
+  preload(m, { quiet: true });
+}, true);
+
+
 // ============================================================================
 // Video editor — cut parts out of a video and save a custom offline copy
 //