feat(scheduling): restrict scheduling module to allowed users only

Only userId 1105261382487539712 and 1116631120763437056 can see the
scheduling tab. Other users see only assets + mileage modules.

- Add userId to frontend AuthState.user type
- App.tsx conditionally includes scheduling module based on user ID
- Backend already returns userId in auth exchange response

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/auth/useAuth.ts

@@ -3,7 +3,7 @@ import { createContext, useContext } from 'react';
 export interface AuthState {
   isLoading: boolean;
   isAuthenticated: boolean;
-  user: { userName: string; permissionLevel: string; depName: string } | null;
+  user: { userId: string; userName: string; permissionLevel: string; depName: string } | null;
   error: string | null;
 }