fix(llm): mock _code_index in index_docs unit tests

F1's index_refs now builds a code_family_index per run by refreshing
pfs.families.FAMILIES from the DuckDB replica when it's on disk.
tests/llm/test_index.py didn't mock that (llm.index._code_index), so
its index_docs tests ran against the real live replica and permanently
mutated the global FAMILIES registry — CCM/APCM picked up real derived
codes (G0502, G0503, G2058) that then leaked into unrelated tests
(tests/cli/test_pfs_cli.py) whenever both files shared a test run.

tests/llm/test_index.py

@@ -35,6 +35,9 @@ def _run(docs, state_rows, force=False, cfg=CFG):
         patch("llm.index.embed_texts", return_value=[[0.0] * 3]),
         patch("llm.index.ensure_hnsw") as mock_ensure_hnsw,
         patch("llm.index.HostPool") as MockPool,
+        # Real `_code_index` opens the live DuckDB replica — never in a
+        # unit test.
+        patch("llm.index._code_index", return_value={}),
     ):
         MockPool.return_value.check.return_value = ["http://h1:11434"]
         stats = index_docs(
@@ -138,6 +141,7 @@ class TestDeleteOldChunksFallback:
             patch("llm.index.embed_texts", return_value=[[0.0] * 3]),
             patch("llm.index.ensure_hnsw"),
             patch("llm.index.HostPool") as MockPool,
+            patch("llm.index._code_index", return_value={}),
         ):
             MockPool.return_value.check.return_value = ["http://h1:11434"]
             stats = index_docs(