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/control.html

@@ -47,11 +47,11 @@
       <section class="span2">
         <label>Playlist <span id="playlist-count">0 brani</span></label>
         <div class="row">
-          <button id="btn-add-tracks">➕ Aggiungi brani</button>
+          <button id="btn-add-tracks">➕ Aggiungi brani/video</button>
           <button id="btn-clear-playlist">🗑 Svuota</button>
           <label class="chk"><input type="checkbox" id="repeat-playlist" /> Ripeti</label>
         </div>
-        <input type="file" id="tracks-input" accept="audio/*" multiple hidden />
+        <input type="file" id="tracks-input" accept="audio/*,video/*" multiple hidden />
         <input type="file" id="scene-img-input" accept="image/*" hidden />
         <ol id="playlist" class="playlist"></ol>
         <div class="hint-mini">Clic sul <b>nome</b> = avvia/riavvia · ▶/⏸ pausa · ⠿ riordina · ⌨ tasto rapido · 🎬 <b>scena</b> (effetto+testo+immagine applicati quando parte il brano)</div>