feat: add background music support and static files mount

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/player.html

@@ -660,6 +660,7 @@ function handle(msg) {
     else showRoundResults(msg);
   }
   else if (msg.type === 'podium') {
+    stopBGM();
     showPodium(msg.leaderboard);
   }
 }
@@ -685,6 +686,7 @@ document.getElementById('join-btn').addEventListener('click', () => {
   }
 
   const display = `${fn} ${ln}`;
+  startBGM();
   ws.send(JSON.stringify({type: 'join', name: display, dept, display}));
 });
 
@@ -787,6 +789,23 @@ function showPodium(lb) {
 
 
 // ── INIT ──────────────────────────────────────────────────────────────────────
+// ── BACKGROUND MUSIC ─────────────────────────────────────────────────────────
+
+let bgmStarted = false;
+function startBGM() {
+  const bgm = document.getElementById('bgm');
+  if (bgmStarted) return;
+  bgmStarted = true;
+  bgm.volume = 0.20;
+  bgm.play().catch(() => {});
+}
+function stopBGM() {
+  const bgm = document.getElementById('bgm');
+  bgm.pause();
+  bgm.currentTime = 0;
+  bgmStarted = false;
+}
+
 window.addEventListener('resize', () => { if (grid) { setupCanvas(); drawGrid(); }});
 connectWS();
 </script>
@@ -800,5 +819,6 @@ connectWS();
   </div>
 </div>
 
+<audio id="bgm" src="/static/music.mp3" loop preload="auto"></audio>
 </body>
 </html>