Fix: Update all old-style imports inside packages to new paths

65 files in klausur-service packages + 3 in backend-lehrer packages
had stale imports referencing deleted shim modules.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/ocr/labeling/upload_routes.py

@@ -17,7 +17,7 @@ from typing import Optional, List
 import uuid
 import os
 
-from metrics_db import (
+from metrics.db import (
     get_ocr_labeling_session,
     add_ocr_labeling_item,
     get_ocr_labeling_item,
@@ -42,7 +42,7 @@ except ImportError:
     pass
 
 try:
-    from training_export_service import TrainingSample, get_training_export_service
+    from training.export_service import TrainingSample, get_training_export_service
 except ImportError:
     pass
 
@@ -271,7 +271,7 @@ async def run_ocr_for_item(item_id: str):
     if ocr_text is None:
         raise HTTPException(status_code=500, detail="OCR failed")
 
-    from metrics_db import get_pool
+    from metrics.db import get_pool
     pool = await get_pool()
     if pool:
         async with pool.acquire() as conn: