test(realtime): add integration tests for collaborative whiteboard features (#60)

[pithva007]

Description

This PR addresses Issue #60 by establishing a comprehensive automated integration testing suite targeting the core Socket.IO real-time features on both the frontend and backend. It strictly guarantees deterministic test execution by avoiding live ports or real database dependencies.

Backend Testing (Jest + socket.io-client)

• Engineered a reusable socketTestClient.js helper that seamlessly binds our Express backend to dynamic ports on-the-fly.
• Implemented robust test coverage validating successful JWT connection lifecycles, unauthorized connection rejections, room membership separation, and the realtime propagation of drawings/strokes across concurrent clients.
• Fully mocked mongoose payloads containing method chaining (like .populate()) to avert any MongoDB cloud lookups.

Frontend Testing (Vitest + React Testing Library)

• Set up lightweight frontend unit tests leveraging Vitest.
• Heavily mocked socket.io-client with a synthetic event emitter architecture allowing test suites to validate internal Whiteboard.jsx state transitions (e.g. broadcasting clear-canvas correctly).
• Asserts strict listener cleanup procedures on component unmount to prevent React memory leaks.

Related Issues

Closes #60

Testing Checklist

• Backend WebSocket connection testing implemented.
• Room isolation and multiple-client connectivity verified.
• Sync events (drawing-stroke, draw-element) verified.
• Frontend synthetic event simulation passes.
• Zero usage of magic sleep functions; tests are strictly event-driven.

CI Workflow Summary

• Created .github/workflows/realtime-tests.yml to automatically execute on push and pull_request against main.
• Strategized npm cache sharing to dramatically optimize workflow velocity.
• Workflow enforces a strict Node.js 18.x LTS baseline matrix and will block merges upon any test suite failures across either directory.

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[KENZY004]

Nice work on this! I tested it locally and all 3 tests are failing because of an Invalid token error. JWT_SECRET is being read before dotenv loads, so move it inside createClient().

Also, stopServer() should properly close the socket server, otherwise Jest force exits because of open handles.

Fix these two and it should be good to go!