feat: implement Fitbit OAuth, Garmin MFA, and optimize segment discovery

- Add Fitbit authentication flow (save credentials, OAuth callback handling)
- Implement Garmin MFA support with successful session/cookie handling
- Optimize segment discovery with new sampling and activity query services
- Refactor database session management in discovery API for better testability
- Enhance activity data parsing for charts and analysis
- Update tests to use testcontainers and proper dependency injection
- Clean up repository by ignoring and removing tracked transient files (.pyc, .db)

FitnessSync/backend/src/api/analysis.py

@@ -20,10 +20,7 @@ from ..utils.config import config
 
 router = APIRouter()
 
-def get_db():
-    db_manager = PostgreSQLManager(config.DATABASE_URL)
-    with db_manager.get_db_session() as session:
-        yield session
+from .status import get_db
 
 class EffortAnalysisData(BaseModel):
     effort_id: int