feat: implement backend API clients for multi-marketplace integration and frontend service layer

backend/app.py

@@ -16,7 +16,9 @@ app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
 
 # Register blueprints (routes)
 from .routes.cases import cases_blueprint
+from .routes.credentials import credentials_blueprint
 app.register_blueprint(cases_blueprint, url_prefix='/api')
+app.register_blueprint(credentials_blueprint, url_prefix='/api')
 
 if __name__ == '__main__':
     # Use host 0.0.0.0 for Docker compatibility, port 5000