Fix IPA spacing + add zone debug logging for marker column issue

1. Ensure space before IPA brackets in cell text: "word[ipa]" → "word [ipa]"
   Applied as final cleanup in grid-build finalization.

2. Add debug logging for zone-word assignment to diagnose why marker
   column cells are empty despite correct column detection.

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

klausur-service/backend/grid_editor_api.py

@@ -347,6 +347,13 @@ async def _build_grid_core(
                     zone_words = _words_in_zone(
                         all_words, pz.y, pz.height, pz.x, pz.width
                     )
+                    if pz.zone_type == "content":
+                        logger.info(
+                            "build-grid zone %d (%s): bounds x=%d..%d y=%d..%d → %d/%d words",
+                            pz.index, pz.zone_type,
+                            pz.x, pz.x + pz.width, pz.y, pz.y + pz.height,
+                            len(zone_words), len(all_words),
+                        )
                     # Filter recovered single-char artifacts in ALL zones
                     # (decorative colored pixel blobs like !, ?, • from
                     # recover_colored_text that don't represent real text)
@@ -1710,6 +1717,16 @@ async def _build_grid_core(
     except ImportError:
         pass
 
+    # --- Ensure space before IPA brackets: "word[ipa]" → "word [ipa]" ---
+    _IPA_NOSPACE_RE = re.compile(r'([a-zA-ZäöüÄÖÜß])(\[[^\]]*[ˈˌːɑɒæɛəɜɪɔʊʌðŋθʃʒɹɡɾ][^\]]*\])')
+    for z in zones_data:
+        for cell in z.get("cells", []):
+            text = cell.get("text", "")
+            if text and "[" in text:
+                fixed = _IPA_NOSPACE_RE.sub(r'\1 \2', text)
+                if fixed != text:
+                    cell["text"] = fixed
+
     # Clean up internal flags before returning
     for z in zones_data:
         for cell in z.get("cells", []):