feat: implement admin API endpoint to suspend users (#13)

[QueenColly]

Closes #13

Summary of Work Done:
Implemented the administrative endpoint to suspend malicious users/drivers, strictly adhering to the requested Controller -> Service -> Model architecture.

Implementation Details:

Routing & Security (backend/src/routes/adminRoutes.ts): Registered PUT /api/v1/admin/users/:id/suspend and protected it using the existing Admin role middleware to ensure strict access control.

Controller (backend/src/controllers/adminController.ts): Handled parameter validation for the user ID and formatted the standard API response.

Service (backend/src/services/adminService.ts): Handled the business logic and database interaction, retrieving the target user via Mongoose and updating their status to suspended. Added robust error handling for scenarios where the user ID does not exist.

Environment & Integration: Connected to the live MongoDB database using the provided .env credentials. No mock data or hardcoded values were used.

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