feat: Add combined track functionality with repository and service layers

- Introduced CombinedTrackModel, CombinedTrackCreate, and CombinedTrackRepository for managing combined tracks.
- Implemented logic to create combined tracks based on existing tracks between two stations.
- Added methods to check for existing combined tracks and retrieve constituent track IDs.
- Enhanced TrackModel and TrackRepository to support OSM ID and track updates.
- Created migration scripts for adding combined tracks table and OSM ID to tracks.
- Updated services and API endpoints to handle combined track operations.
- Added tests for combined track creation, repository methods, and API interactions.

backend/app/api/__init__.py

@@ -4,9 +4,11 @@ from backend.app.api.auth import router as auth_router
 from backend.app.api.health import router as health_router
 from backend.app.api.network import router as network_router
 from backend.app.api.stations import router as stations_router
+from backend.app.api.tracks import router as tracks_router
 
 router = APIRouter()
 router.include_router(health_router, tags=["health"])
 router.include_router(auth_router)
 router.include_router(network_router)
 router.include_router(stations_router)
+router.include_router(tracks_router)