feat: add multi-user support for favorites management and room clock synchronization

- Implemented a new API endpoint for retrieving and managing user favorites in /api/users.
- Added functionality for admins to edit the shared "main" user's favorites.
- Created a one-shot DB smoke test script for verifying multi-user kiosk migrations.
- Introduced a RoomClock class for synchronizing server time across clients using WebSocket.

server/scripts/check-multiuser.js

@@ -0,0 +1,24 @@
+// One-shot DB smoke test for the multi-user kiosk migrations.
+import { initDb, getDb } from '../db/index.js';
+import { ensureMainUser, getMainUser } from '../auth.js';
+import { app } from 'electron';
+
+initDb(process.env.DB_PATH || './data/db/oradio.sqlite');
+const db = getDb();
+ensureMainUser(process.env.MAIN_USER || 'morphix');
+
+const userCols = db.prepare("PRAGMA table_info(users)").all().map((c) => c.name);
+const deviceCols = db.prepare("PRAGMA table_info(kiosk_devices)").all().map((c) => c.name);
+const wlCols = db.prepare("PRAGMA table_info(kiosk_device_users)").all().map((c) => c.name);
+const roomStateCols = db.prepare("PRAGMA table_info(room_state)").all().map((c) => c.name);
+const users = db.prepare('SELECT id, username, role, is_main, avatar_color, avatar_emoji FROM users').all();
+const mainCount = db.prepare('SELECT count(*) AS c FROM users WHERE is_main = 1').get().c;
+
+console.log('users cols:           ', userCols.join(', '));
+console.log('kiosk_devices cols:   ', deviceCols.join(', '));
+console.log('kiosk_device_users:   ', wlCols.join(', '));
+console.log('room_state cols:      ', roomStateCols.join(', '));
+console.log('users:                ', JSON.stringify(users, null, 2));
+console.log('main user count:      ', mainCount);
+console.log('getMainUser():        ', getMainUser());
+app.quit();