Fix IPA continuation: don't replace normal text with IPA

Text like "Betonung auf der 1. Silbe: profit ['profit]" was
incorrectly detected as garbled IPA and replaced with generated
IPA transcription of the previous row's example sentence.

Added guard: if the cell text contains >=3 recognizable words
(3+ letter alpha tokens), it's normal text, not garbled IPA.
Garbled IPA is typically short and has no real dictionary words.

Fixes: Row 13 C3 showing IPA instead of pronunciation hint text.

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

klausur-service/backend/grid_build_core.py

@@ -1112,6 +1112,13 @@ async def _build_grid_core(
                         # Has real IPA symbols → already fixed or valid
                         if any(c in _REAL_IPA_CHARS for c in cell_text):
                             continue
+                        # Guard: if text contains multiple real words, it's
+                        # normal text (e.g. "Betonung auf der 1. Silbe:
+                        # profit"), not garbled IPA.  Garbled IPA is
+                        # typically short and has no recognizable words.
+                        _words_in_text = re.findall(r'[A-Za-zÄÖÜäöüß]{3,}', cell_text)
+                        if len(_words_in_text) >= 3:
+                            continue
 
                     # Find headword in previous row, same column
                     prev_ri = rows_sorted[idx - 1]["index"]