fix: column_text Typ fuer Sub-Sessions in Korrektur-Tabelle

_cells_to_vocab_entries kannte column_text nicht, daher wurden
keine Eintraege erzeugt. Jetzt mappt column_text -> 'text' Feld.

Frontend: column_text in FIELD_LABELS/COL_TYPE_TO_FIELD/COL_TYPE_COLOR.
Label: "Tabelle" statt "Vokabeltabelle" fuer Sub-Sessions.

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

klausur-service/backend/cv_cell_grid.py

@@ -1241,6 +1241,7 @@ def _cells_to_vocab_entries(
         'column_example': 'example',
         'page_ref': 'source_page',
         'column_marker': 'marker',
+        'column_text': 'text',  # generic single-column (box sub-sessions)
     }
     bbox_key_map = {
         'column_en': 'bbox_en',
@@ -1248,6 +1249,7 @@ def _cells_to_vocab_entries(
         'column_example': 'bbox_ex',
         'page_ref': 'bbox_ref',
         'column_marker': 'bbox_marker',
+        'column_text': 'bbox_text',
     }
 
     # Group cells by row_index
@@ -1264,6 +1266,7 @@ def _cells_to_vocab_entries(
             'english': '',
             'german': '',
             'example': '',
+            'text': '',  # generic single-column (box sub-sessions)
             'source_page': '',
             'marker': '',
             'confidence': 0.0,
@@ -1273,6 +1276,7 @@ def _cells_to_vocab_entries(
             'bbox_ex': None,
             'bbox_ref': None,
             'bbox_marker': None,
+            'bbox_text': None,
             'ocr_engine': row_cells[0].get('ocr_engine', '') if row_cells else '',
         }