feat(database): add migration and sync-db scripts to deployment process

- Introduced a new npm script for database migrations in package.json.
- Updated update-backend.sh to execute migrations and conditionally run legacy sync-db based on environment variable.
- Enhanced syncDatabase.js to skip initialization routines if APP_INIT_ON_START is not set, promoting best practices for schema changes during deployment.

update-backend.sh

@@ -62,4 +62,14 @@ echo "Running database synchronization..."
 cd "$BACKEND_DIR"
 export STAGE="$STAGE"
 
+echo "Führe Migrationen aus..."
+npm run db:migrate
+
+if [ "${RUN_LEGACY_SYNC_DB_ON_DEPLOY:-0}" = "1" ]; then
+  echo "RUN_LEGACY_SYNC_DB_ON_DEPLOY=1 gesetzt -> führe zusätzlich legacy sync-db aus..."
+  npm run sync-db
+else
+  echo "Legacy sync-db übersprungen (Standard)."
+fi
+
 echo "Backend update completed!"