feat: Add Health Check Endpoint for System Monitoring

[gitit24x7]

Currently, there is no standardized way to verify if the DocuHub backend is healthy and running. This makes it difficult to set up automated monitoring or uptime checks (e.g., via UptimeRobot, Railway, or AWS health checks).

I propose adding a dedicated health check endpoint at /api/health.

in this format:
- Status:200 OK`
- Body:
```json
{
"status": "ok",
"timestamp": "2024-02-18T10:00:00.000Z",
"version": "0.1.0"
}
````

• This endpoint should be lightweight and not perform heavy database operations.
• It will ensure 100% observability for production deployments.