fix(wiki): token-boundary grounding match + sharper ref-list filter (C-6, R-2)

- C-6: the content-5-gram check used 'gram in src' on space-joined strings, so the
  first/last gram token could match a prefix/suffix of a longer chunk word
  ('set' inside 'subset'). Both gram and chunk are now space-padded, so a match
  requires whole-token alignment. Regression test added.
- R-2: the reference-list filter's author pattern ('Surname, I.') also matched
  'Theorem A.'/'Lemma B.', so theorem-dense chunks could be dropped as a
  bibliography. The pattern now excludes common math-structure words.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/wiki/test_compile.py

@@ -230,6 +230,30 @@ def test_grounding_guard_robust_to_trailing_comma() -> None:
     assert result[0].grounded is True
 
 
+def test_grounding_guard_no_substring_bleed_across_tokens() -> None:
+    """A 5-gram must match whole tokens, not bleed into a longer chunk word (audit C-6).
+
+    The chunk contains 'subset'; a claim whose first token is 'set' must NOT ground
+    by substring-matching the suffix of 'subset'.
+    """
+    chunks = [
+        {
+            "id": 99,
+            "paper_id": "p",
+            "ord": 0,
+            "bibkey": "TestBib",
+            "content": "the subset conformal map energy functional is minimized here",
+        }
+    ]
+    claim = Claim(
+        text="the set conformal map energy functional",
+        bibkey="TestBib",
+        locator="chunk 0",
+    )
+    result = _run_grounding_guard([claim], chunks)
+    assert result[0].grounded is False
+
+
 # ---------------------------------------------------------------------------
 # _inject_cross_refs
 # ---------------------------------------------------------------------------