test: Add backend unit tests

[namann5]

🧪 Feature Request — Testing Infrastructure

Description

The project currently has zero test files in the entire codebase. The CI pipeline
(ci.yml) only runs ruff and mypy for the backend — there is no pytest step.
This means broken logic can be merged without any automated safety net.

Current CI (backend jobs)

• ✅ Ruff linting
• ✅ Ruff format check
• ✅ mypy type checking
• ❌ No unit/integration tests

What's Missing

• No tests/ directory in backend/
• No pytest or pytest-asyncio in dev dependencies
• No test step in .github/workflows/ci.yml

Suggested Fix

1. Add test dependencies to pyproject.toml:

[tool.uv.dev-dependencies]
pytest = ">=8.0"
pytest-asyncio = ">=0.23"
httpx = ">=0.27"   # for FastAPI TestClient

[RITVIKKAMASETTY]

@namann5 this is a great issue
you can start working on this remember to have clean commit history not 7000+ lines commit in single commit

go from unit test to integration testing

[sathwikshetty33]

@namann5 Even I would suggest adding unit tests for now, keep the commits minimal covering the coherent change.

[namann5]

@RITVIKKAMASETTY Yea, i'll start working on this from tommorow onwards, cz my last exam.

[namann5]

@sathwikshetty33 @RITVIKKAMASETTY
Just a gentle reminder regarding PR #104. Looking forward to your review whenever possible. Thank you! 🚀

[ShreeniG99]

I'd like to help with this.
I've gone through the backend routes and I'd like to start with unit tests for the interview scheduling and evaluation endpoints -mocking the DB session and LLM calls so that tests can run fast without external dependencies. I'll follow pytest conventions.
Could you assign this to me pleasee?