fix: resolve circular import with lazy import for _build_reference_snapshot

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

klausur-service/backend/grid_editor_api.py

@@ -31,7 +31,6 @@ from ocr_pipeline_session_store import (
     get_session_image,
     update_session_db,
 )
-from ocr_pipeline_regression import _build_reference_snapshot
 
 logger = logging.getLogger(__name__)
 
@@ -2816,6 +2815,9 @@ async def build_grid(session_id: str):
         raise HTTPException(status_code=400, detail=str(e))
 
     # Save automatic grid snapshot for later comparison with manual corrections
+    # Lazy import to avoid circular dependency with ocr_pipeline_regression
+    from ocr_pipeline_regression import _build_reference_snapshot
+
     wr = session.get("word_result") or {}
     engine = wr.get("ocr_engine", "")
     if engine in ("kombi", "rapid_kombi"):