Add minimal tests for DB connectivity

[Neha20072002]

Add minimal tests for DB connectivity

Introduce a tiny test that ensures the SQLite DB connects and STUDENT table exists.
Suggest using pytest and add it as a dev dependency; include a GitHub issue to add CI later.
New files under tests/.

[SK8-infi]

Please assign. would like to work.

[Neha20072002]

Assigned @SK8-infi