- Add max_devices column to users table (default: 10)
- Add UpdateUserMaxDevices database query
- Add CountUserDevices database query
- Add UpdateUserMaxDevices handler with validation (1-100 devices)
- Add PUT /api/auth/users/:id/max-devices endpoint (admin only)
- Update UserList struct to include max_devices field
- Validate user ID format and max_devices range
- Return appropriate errors for invalid requests