fix: configure CI database connection properly

- Add dotenv loading to Django settings
- Update CI workflow to use correct environment variables
- Set POSTGRES_* variables instead of DATABASE_URL
- Add environment variables to all Django management commands
- Fixes CI test failures due to database connection issues

app/core/settings.py

@@ -1,5 +1,9 @@
 import os
 from pathlib import Path
+from dotenv import load_dotenv
+
+# Load environment variables from .env file
+load_dotenv()
 
 BASE_DIR = Path(__file__).resolve().parent.parent