Restructure: Move 47 cv_* files into ocr/ package

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

klausur-service/backend/ocr/cell_grid/vocab.py

@@ -10,13 +10,13 @@ DATENSCHUTZ: Alle Verarbeitung erfolgt lokal.
 import logging
 from typing import Any, Dict, List
 
-from cv_ocr_engines import (
+from ..engines.engines import (
     _attach_example_sentences,
     _fix_phonetic_brackets,
     _split_comma_entries,
 )
-from cv_cell_grid_legacy import build_cell_grid
-from cv_cell_grid_merge import (
+from .legacy import build_cell_grid
+from .merge import (
     _merge_continuation_rows,
     _merge_phonetic_continuation_rows,
     _merge_wrapped_rows,