E2E tests

[CapoMK25]

Brief description

Added a baseline setup and configuration for End-to-End (E2E) testing against API endpoints.

Change list

• Added README.md in test/ documenting E2E execution, local dependencies, and test structure

• Updated npm run test:e2e script flags in package.json (--runInBand, --forceExit) to ensure clean execution all around

• Fixed NestJS platform WebSocket driver dependency (@nestjs/platform-socket.io)

• Resolved background service teardown issues (MQTT reconnect loops and MongoDB handle cleanup) in app.e2e-spec.ts

NOTE:

This is just the foundations, since issue #480 advocated for only a baseline setup. Future PRs can add dedicated feature suites (e.g., auth, profile, clan) using app.e2e-spec.ts as a template. Similar setup as migrate-mongo previously.

[codecov-alt]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 1 file with indirect coverage changes

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[tickBit]

Nice work 👍 ! Approved.