Restructure: Move grid_* + vocab_* into packages (klausur-service)

grid/ package (16 files):
  grid/build/   — core, zones, cleanup, text_ops, cell_ops, finalize
  grid/editor/  — api, helpers, columns, filters, headers, zones

vocab/ package (10 files):
  vocab/worksheet/ — api, models, extraction, generation, ocr, upload, analysis, compare
  vocab/           — session_store, learn_bridge

26 backward-compat shims. Internal imports relative. RAG untouched.

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

klausur-service/backend/grid/editor/helpers.py

@@ -0,0 +1,58 @@
+"""
+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
+continue to work without changes.
+
+Sub-modules:
+  - columns  — column detection, cross-column splitting, marker merging
+  - filters  — word/zone filtering, border ghosts, decorative margins
+  - headers  — header/heading detection, colspan detection
+  - zones    — vertical dividers, zone splitting/merging, zone grid building
+
+Lizenz: Apache 2.0 (kommerziell nutzbar)
+DATENSCHUTZ: Alle Verarbeitung erfolgt lokal.
+"""
+
+# --- Re-export: columns ---------------------------------------------------
+from .columns import (  # noqa: F401
+    _is_recognized_word,
+    _split_cross_column_words,
+    _cluster_columns_by_alignment,
+    _MARKER_CHARS,
+    _merge_inline_marker_columns,
+)
+
+# --- Re-export: filters ----------------------------------------------------
+from .filters import (  # noqa: F401
+    _filter_border_strip_words,
+    _GRID_GHOST_CHARS,
+    _filter_border_ghosts,
+    _flatten_word_boxes,
+    _words_in_zone,
+    _get_content_bounds,
+    _filter_decorative_margin,
+    _filter_footer_words,
+    _filter_header_junk,
+)
+
+# --- Re-export: headers ----------------------------------------------------
+from .headers import (  # noqa: F401
+    _detect_heading_rows_by_color,
+    _detect_heading_rows_by_single_cell,
+    _detect_header_rows,
+    _detect_colspan_cells,
+)
+
+# --- Re-export: zones -------------------------------------------------------
+from .zones import (  # noqa: F401
+    _PIPE_RE_VSPLIT,
+    _detect_vertical_dividers,
+    _split_zone_at_vertical_dividers,
+    _merge_content_zones_across_boxes,
+    _build_zone_grid,
+)
+
+# --- Re-export from cv_words_first (used by cv_box_layout.py) ---------------
+from cv_words_first import _cluster_rows  # noqa: F401