Add master display UI with audio output management and styling

- Implement main.js for the master display functionality, including WebSocket connection, audio output management, and state handling.
- Create style.css for the master display's visual design, ensuring a cohesive look and feel with a dark theme and responsive layout.
- Integrate device management with a fallback for non-Electron environments, allowing users to select audio outputs.
- Add features for managing favorites, including toggling favorites and filtering by genre.
- Enhance user experience with a responsive favorites grid and drag-to-scroll functionality.

web/style.css

@@ -313,6 +313,49 @@ textarea {
     align-items: center;
 }
 
+/* Room sync pill: room picker + peer count + here/follow mode toggle. */
+.room-pill {
+    display: inline-flex;
+    align-items: center;
+    gap: 6px;
+    padding: 4px 8px;
+    height: 36px;
+    background: var(--bg-2);
+    border: 1px solid var(--line);
+    border-radius: 999px;
+    font-size: 12px;
+}
+.room-pill .room-icon { opacity: .7; }
+.room-pill .room-select {
+    background: transparent;
+    color: var(--fg);
+    border: none;
+    outline: none;
+    font-size: 12px;
+    max-width: 140px;
+}
+.room-pill .room-peers {
+    color: var(--muted-2);
+    font-variant-numeric: tabular-nums;
+    min-width: 18px;
+    text-align: center;
+}
+.room-pill .room-mode {
+    height: 26px;
+    padding: 0 10px;
+    border-radius: 999px;
+    border: 1px solid var(--line);
+    background: var(--bg-1);
+    color: var(--fg);
+    font-size: 11px;
+    cursor: pointer;
+}
+.room-pill .room-mode.follow-room {
+    background: linear-gradient(180deg, rgba(255, 122, 61, 0.18), rgba(255, 122, 61, 0.08));
+    color: var(--accent-2);
+    border-color: rgba(255, 122, 61, 0.30);
+}
+
 .search {
     width: 220px;
     padding: 8px 12px;