Fix hyphen-join: strip trailing punctuation from continuation word

The next-row word "künden," had a trailing comma, causing dictionary
lookup to fail for "verkünden,". Now strips .,;:!? before joining.

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

klausur-service/backend/tests/test_gutter_repair.py

@@ -126,6 +126,21 @@ class TestTryHyphenJoin:
         assert _try_hyphen_join("", "word") is None
         assert _try_hyphen_join("word", "") is None
 
+    def test_join_strips_trailing_punctuation(self):
+        # "ver" + "künden," → should still find "verkünden" despite comma
+        result = _try_hyphen_join("ver-", "künden,")
+        assert result is not None
+        joined, missing, conf = result
+        assert joined == "verkünden"
+
+    def test_join_with_missing_chars_and_punctuation(self):
+        # "ve" + "künden," → needs "r" in between, comma must be stripped
+        result = _try_hyphen_join("ve", "künden,", max_missing=2)
+        assert result is not None
+        joined, missing, conf = result
+        assert joined == "verkünden"
+        assert "r" in missing
+
 
 @needs_spellchecker
 class TestTrySpellFix: