Fix IPA continuation: only process fully-bracketed cells, keep phrasal verb particles

Two fixes:
1. Step 5d now only treats cells as continuation when text is entirely
   inside brackets (e.g. "[n, nn]"). Cells with headwords outside brackets
   (e.g. "employee [im'ploi:]") are no longer overwritten.
2. fix_ipa_continuation_cell no longer skips grammar words like "down" —
   they are part of the headword in phrasal verbs like "close sth. down".

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

klausur-service/backend/tests/test_grid_editor_api.py

@@ -499,3 +499,24 @@ class TestGarbledIpaDetection:
         )
         assert fixed != "[1uedtX,1]"
         assert "ɪkwˈɪpmənt" in fixed  # equipment IPA
+
+    def test_fix_continuation_close_down(self):
+        """IPA continuation for 'close sth. down' → IPA for both words."""
+        fixed = fix_ipa_continuation_cell(
+            "[klaoz 'daun]", "close sth. down", pronunciation="british",
+        )
+        assert fixed != "[klaoz 'daun]"
+        assert "klˈəʊs" in fixed   # close IPA
+        assert "dˈaʊn" in fixed    # down IPA — must NOT be skipped
+
+    def test_headword_with_brackets_not_continuation(self):
+        """'employee [im'ploi:]' has a headword outside brackets → not garbled.
+
+        _text_has_garbled_ipa returns True (has ':'), but Step 5d should
+        skip this cell because text doesn't start with '['.
+        """
+        # The garbled check still triggers (has IPA-like ':')
+        assert _text_has_garbled_ipa("employee [im'ploi:]") is True
+        # But text does NOT start with '[' — Step 5d bracket guard blocks it
+        text = "employee [im'ploi:]"
+        assert not (text.strip().startswith('[') and text.strip().endswith(']'))