Fix word-split: handle IPA brackets, contractions, and tiebreaker

1. Strip IPA brackets [ipa] before attempting word split, so
   "makeadecision[dɪsˈɪʒən]" is processed as "makeadecision"
2. Handle contractions: "solet's" → split "solet" → "so let" + "'s"
3. DP tiebreaker: prefer longer first word when scores are equal
   ("task is" over "ta skis")

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

klausur-service/backend/grid_editor_api.py

@@ -1752,8 +1752,27 @@ async def _build_grid_core(
                     changed = False
                     for token in text.split():
                         # Try splitting pure-alpha tokens >= 4 chars
-                        clean = token.rstrip(".,!?;:'\")")
-                        suffix = token[len(clean):]
+                        # Strip trailing punctuation AND IPA brackets
+                        clean = token
+                        # Remove trailing IPA like [dɪsˈɪʒən] first
+                        bracket_pos = clean.find('[')
+                        suffix_ipa = ""
+                        if bracket_pos > 0:
+                            suffix_ipa = clean[bracket_pos:]
+                            clean = clean[:bracket_pos]
+                        suffix_punct = ""
+                        stripped = clean.rstrip(".,!?;:'\")")
+                        if stripped != clean:
+                            suffix_punct = clean[len(stripped):]
+                            clean = stripped
+                        suffix = suffix_punct + suffix_ipa
+                        # Handle contractions: "solet's" → try "solet" + "'s"
+                        contraction = ""
+                        if "'" in clean and clean.index("'") >= 2:
+                            apos_pos = clean.index("'")
+                            contraction = clean[apos_pos:]
+                            clean = clean[:apos_pos]
+                            suffix = contraction + suffix
                         if len(clean) >= 4 and clean.isalpha():
                             split = _try_split_merged_word(clean)
                             if split: