Playlist supports video tracks (full-screen video + audio through the analyser)

Audio and video files can both be added to the playlist; video tracks play
full-screen with their audio routed through the analyser (visuals/waveform
react), have duration/progress, and are included in recordings. Persisted.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/output.html

@@ -13,6 +13,9 @@
   <!-- Video layer (VJ loop) that blends with the generated visuals -->
   <video id="bg-video" class="bg-video" loop muted playsinline></video>
 
+  <!-- Playlist video track (full screen, with its own audio) -->
+  <video id="track-video" class="track-video" playsinline></video>
+
   <!-- Image overlay layer -->
   <div id="overlay-images"></div>