feat : added health check endpoint for backend server

[tmdeveloper007]

Summary of What Has Been Done

Added a public GET /health endpoint to the backend that returns a JSON response with the server status and a timestamp.

Changes Made

1. Created backend/routes/healthRoutes.js:
   • GET / returns { status: "ok", timestamp: "<ISO timestamp>" } with HTTP 200
   • No authentication required (public endpoint for monitoring tools)
2. Updated backend/src/server.js:
   • Imported healthRouter from the new routes file
   • Mounted it at the /health path

Impact it Made

• Enables uptime monitoring tools (e.g., healthchecks.io, Pingdom) to verify backend availability
• Allows load balancers and reverse proxies to perform health checks
• Provides a lightweight diagnostics endpoint for debugging and observability

Closes #1894

Note: Please assign this PR to the tmdeveloper007 account.