- Introduced the Endurain integration, allowing users to connect their self-hosted Endurain instance for activity browsing and GPX import.
- Added `EndurainIntegration` model, serializer, and viewset to manage user connections and activities.
- Implemented MFA support for Endurain login, including token handling and validation.
- Enhanced activity handling in `ActivityViewSet` to prioritize user-provided elevation data over GPX-derived values.
- Updated environment configuration and documentation to include Endurain integration details.
- Added tests for Endurain services and integration functionality to ensure reliability and correctness.
- Improved throttling for Endurain authentication to enhance security and performance.
