Complete spec: Code alignment and documentation cleanup

- Ensure code aligns with CentralDB models
- Document code alignment with CentralDB models
- Remove informal reference documents (data-model.md, DB_API_SPEC.json, GARMINSYNC_SPEC.md)
- Run linters and formatters (black, isort, mypy)
- Update project configuration files
- Add .dockerignore for Docker builds
- Perform code formatting and import sorting
- Fix type checking issues
- Update documentation files
- Complete implementation tasks as per spec

backend/tests/api/test_garmin_sync_api.py

@@ -1,6 +1,7 @@
+from fastapi.testclient import TestClient
+
 from backend.src.main import app
 from backend.src.services.sync_manager import current_sync_job_manager
-from fastapi.testclient import TestClient
 
 client = TestClient(app)