Add player functionality with HLS support and API integration

- Implemented a new Player class in player.js to handle audio playback, including HLS support using hls.js.
- Created a shared API module in api.js for making HTTP requests with proper error handling.
- Added DOM utility functions in dom.js for creating and clearing elements.
- Introduced WebSocket connection handling in ws.js for real-time updates.
- Developed a comprehensive CSS stylesheet for styling the application, including a high-contrast theme.

server/ws.js

@@ -0,0 +1,56 @@
+import { WebSocketServer } from 'ws';
+import { getUserBySession, readSessionToken } from './auth.js';
+
+// per-user channel hub: any client of user U receives messages targeted to U.
+const channels = new Map(); // userId -> Set<ws>
+
+export function attachWs(server) {
+  const wss = new WebSocketServer({ noServer: true });
+
+  server.on('upgrade', (req, socket, head) => {
+    if (!req.url.startsWith('/ws')) return socket.destroy();
+    const token = readSessionToken(req);
+    const user = getUserBySession(token);
+    if (!user) {
+      socket.write('HTTP/1.1 401 Unauthorized\r\n\r\n');
+      socket.destroy();
+      return;
+    }
+    wss.handleUpgrade(req, socket, head, (ws) => {
+      ws.user = user;
+      addClient(user.id, ws);
+      ws.on('close', () => removeClient(user.id, ws));
+      ws.on('message', (raw) => {
+        let msg;
+        try { msg = JSON.parse(raw.toString()); } catch { return; }
+        // Re-broadcast every message to all connections of the same user.
+        // (e.g. phone sends `{type:"command", action:"play", stationId:7}` → kiosk receives)
+        broadcastToUser(user.id, msg, ws);
+      });
+      ws.send(JSON.stringify({ type: 'hello', user: { id: user.id, username: user.username, role: user.role } }));
+    });
+  });
+
+  return wss;
+}
+
+function addClient(userId, ws) {
+  if (!channels.has(userId)) channels.set(userId, new Set());
+  channels.get(userId).add(ws);
+}
+function removeClient(userId, ws) {
+  const set = channels.get(userId);
+  if (!set) return;
+  set.delete(ws);
+  if (!set.size) channels.delete(userId);
+}
+
+export function broadcastToUser(userId, msg, except) {
+  const set = channels.get(userId);
+  if (!set) return;
+  const payload = JSON.stringify(msg);
+  for (const ws of set) {
+    if (ws === except) continue;
+    if (ws.readyState === ws.OPEN) ws.send(payload);
+  }
+}