Protect page references from junk-row removal

Rows containing only a page reference (p.55, S.12) were removed as
"oversized stubs" (Rule 2) when their word-box height exceeded the
median. Now skips Rule 2 if any word matches the page-ref pattern.

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

klausur-service/backend/grid_editor_api.py

@@ -615,10 +615,15 @@ async def _build_grid_core(
             # Rule 2: oversized stub — ≤3 words, short total text,
             # and word height > 1.8× median (page numbers, stray marks,
             # OCR from illustration labels like "SEA &")
+            # Skip if any word looks like a page reference (p.55, S.12).
             if len(row_wbs) <= 3:
                 total_text = "".join((wb.get("text") or "").strip() for wb in row_wbs)
                 max_h = max((wb.get("height", 0) for wb in row_wbs), default=0)
-                if len(total_text) <= 5 and max_h > median_wb_h * 1.8:
+                has_page_ref = any(
+                    re.match(r'^[pPsS]\.?\s*\d+$', (wb.get("text") or "").strip())
+                    for wb in row_wbs
+                )
+                if len(total_text) <= 5 and max_h > median_wb_h * 1.8 and not has_page_ref:
                     junk_row_indices.add(ri)
                     continue