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/alembic.ini

@@ -1,6 +1,6 @@
 [alembic]
 script_location = migrations
-sqlalchemy.url = postgresql+psycopg://railgame:railgame@localhost:5432/railgame
+sqlalchemy.url = postgresql+psycopg://railgame:railgame@localhost:5432/railgame_dev
 
 [loggers]
 keys = root,sqlalchemy,alembic