refactor: define backend environment variables directly in CI workflow instead of using an env file.

Author: HackyCoder0951

.github/workflows/ci.yml

@@ -31,8 +31,9 @@ jobs:
           pip install -r backend/requirements.txt
 
       - name: Start Backend
-        env_file:
-          - ./backend/.env
+        env:
+          MONGO_URI: mongodb://localhost:27017
+          SECRET_KEY: test-secret
         run: |
           cd backend
           uvicorn app.main:app --host 0.0.0.0 --port 8000 &