Fix colspan text + box row fields for GridTable compatibility

Colspan: use original word-block text instead of split cell texts.
Prevents "euros a nd cents" from split_cross_column_words.

Box rows: add is_header field (was undefined, causing GridTable
rendering issues). Add y_min_px/y_max_px to header_only rows.
These missing fields caused empty rows with only row numbers visible.

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

klausur-service/backend/cv_box_layout.py

@@ -177,7 +177,12 @@ def build_box_zone_grid(
         ).strip()
         return {
             "columns": [{"col_index": 0, "index": 0, "label": "column_text", "col_type": "column_1"}],
-            "rows": [{"index": 0, "row_index": 0, "y_min": box_y, "y_max": box_y + box_h, "y_center": box_y + box_h / 2}],
+            "rows": [{"index": 0, "row_index": 0,
+                       "y_min": box_y, "y_max": box_y + box_h, "y_center": box_y + box_h / 2,
+                       "y_min_px": box_y, "y_max_px": box_y + box_h,
+                       "y_min_pct": round(box_y / img_h * 100, 2) if img_h else 0,
+                       "y_max_pct": round((box_y + box_h) / img_h * 100, 2) if img_h else 0,
+                       "is_header": True}],
             "cells": [{
                 "cell_id": f"Z{zone_index}_R0C0",
                 "row_index": 0,
@@ -211,11 +216,11 @@ def build_box_zone_grid(
                 "y_min": y_min,
                 "y_max": y_max,
                 "y_center": y_center,
-                # GridTable expects _px and _pct variants
                 "y_min_px": y_min,
                 "y_max_px": y_max,
                 "y_min_pct": round(y_min / img_h * 100, 2) if img_h else 0,
                 "y_max_pct": round(y_max / img_h * 100, 2) if img_h else 0,
+                "is_header": False,
             }
             rows.append(row)