Update environment variable loading to allow overrides

- Modified load_dotenv() calls in multiple files to include override=True, ensuring that .env variables can replace existing environment variables.
- Updated ota_storage.py to use default values for OTA upload directories, improving clarity and maintainability.
- Enhanced get_ota_upload_dir() function to read environment variables dynamically, ensuring accurate directory paths based on the current environment.

backend/main.py

@@ -10,7 +10,7 @@ from routes.auth import router as auth_router
 from security import get_current_user
 
 # Load environment variables
-load_dotenv()
+load_dotenv(override=True)
 
 # Configure logging
 logging.basicConfig(