Backend:
- Add GET /users/roles endpoint (list all roles)
- Add GET /users/depts endpoint (list all departments)
Frontend:
- Add user.ts API client (getUsers, createUser, updateUser, deleteUser, getRoles, getDepts)
- Rewrite System.vue with full user CRUD:
- User list table with pagination
- Add User button + dialog form
- Edit user (username disabled, password hidden)
- Delete user (disabled for superadmin)
- Role and department dropdowns
- Status radio buttons
hiderfong