Fix CI: set PYTHONPATH=. to resolve backend module imports in tests

Author: DHANUSHGCODE

.github/workflows/ci.yml

@@ -17,6 +17,8 @@ jobs:
           pip install -r backend/requirements.txt
           pip install pytest pytest-cov httpx
       - name: Run backend tests
+        env:
+          PYTHONPATH: .
         run: |
           pytest backend/tests/ --cov=backend