feat: serialize official record imports

apps/api/app/main.py

@@ -22,7 +22,7 @@ from .activity import activity_rows
 from .database import get_session
 from .config import settings
 from .community_review import ExternalReviewError, map_observation, publish_observation, reject_observation
-from .importer import ImportSourceError, import_records, normalize
+from .importer import ImportAlreadyRunning, ImportSourceError, import_records, normalize
 from .logging_config import configure_logging
 from .models import Bait, BaitKind, CatchReport, ExternalObservation, Fish, ModerationEvent, ModerationStatus, OfficialRecordImport, SourceType, Spot, SubmissionAttempt, Waterbody
 from .readiness import readiness_report
@@ -200,6 +200,8 @@ def admin_start_official_import(db: Db, _: Annotated[str, Depends(_admin)]) -> O
             region=settings.official_records_region,
             category=settings.official_records_category,
         )
+    except ImportAlreadyRunning as exc:
+        raise HTTPException(status_code=409, detail=str(exc)) from exc
     except (ImportSourceError, httpx.HTTPError) as exc:
         raise HTTPException(status_code=502, detail=f"official records import failed: {exc}") from exc