Fix database migrations - run from app container instead of volume mount

- Removed migrations volume mount from docker-compose.yml
- Added automatic migration runner in server.js on startup
- Migrations now run from files built into Docker image
- Fixes 'relation does not exist' errors

docker-compose.yml

@@ -11,7 +11,6 @@ services:
       POSTGRES_PASSWORD: ${DB_PASSWORD:-changeme123}
     volumes:
       - postgres_data:/var/lib/postgresql/data
-      - ./migrations:/docker-entrypoint-initdb.d
     ports:
       - "5432:5432"
     healthcheck: