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/grid/editor/helpers.py

@@ -2,7 +2,7 @@
 Grid Editor helper functions — barrel re-export module.
 
 This file re-exports all public symbols from the split sub-modules
-so that existing ``from grid_editor_helpers import ...`` statements
+so that existing ``from grid.editor.helpers import ...`` statements
 continue to work without changes.
 
 Sub-modules:
@@ -55,4 +55,4 @@ from .zones import (  # noqa: F401
 )
 
 # --- Re-export from cv_words_first (used by cv_box_layout.py) ---------------
-from cv_words_first import _cluster_rows  # noqa: F401
+from ocr.words_first import _cluster_rows  # noqa: F401