Created API modules for users and roles management:
- Added src/api/roles.ts with getAllRoles, getRoleById, createRole, etc.
- Added src/api/users.ts with getAllUsers, createUser, updateUser, etc.
Updated UsersPage to fetch data from backend:
- Fetch roles from /api/roles endpoint on mount
- Fetch users from /api/users endpoint on mount
- Integrated createUser API call with form submission
- Added proper validation and error handling
- Split name field into firstName and lastName for API compatibility
- Added loading states and refresh functionality
