feat(pair-corpus-honesty): add vibe-py, vfc-js and agent-vfc slices with mechanism vocabulary

Tasks 1.1, 5.1, 5.2, 5.4 and the data half of 5.3.

- mechanisms.toml: closed vocabulary v1 (20 ids) every expected row cites.
- vibe-py: 35 Real-Vuln-Benchmark pairs (Apache-2.0), human provenance only
  because the LLM-generated repositories carry no license (escalated).
- vfc-js: 17 Node fix-commit pairs harvested upstream (MIT/Apache-2.0),
  SecBench.js itself is not vendored (no license); sinks derived on 13/17.
- agent-vfc: 29 agent-trailer fixes as catalog-candidates.toml plus
  REVIEW.md; the loaded catalog stays empty until a human reviews them.
- datasets.toml and README document every slice and its review status.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

benchmarks/pairs/vibe-py/vulnpy-cmdi-do-subprocess-popen/fixed.py

@@ -0,0 +1,21 @@
+# Provenance: Contrast-Security-OSS/vulnpy do_subprocess_popen (fixed).
+# repo: Contrast-Security-OSS/vulnpy
+# commit: d1d0f64c06f038fe59a049e0e6001bfaf9839697
+# parent: d1d0f64c06f038fe59a049e0e6001bfaf9839697
+# commit_url: https://github.com/Contrast-Security-OSS/vulnpy/blob/d1d0f64c06f038fe59a049e0e6001bfaf9839697/src/vulnpy/trigger/cmdi.py#L10
+# cve: 
+# license: MIT
+# function: do_subprocess_popen
+# relpath: src/vulnpy/trigger/cmdi.py
+# provenance: human
+# mechanism: source_reaches_sink
+
+def _execute(db_func):
+    try:
+        db_connection = _db_reset()
+        cursor = db_connection.cursor()
+        db_func(cursor)
+        all_rows = cursor.execute(SELECT_ALL)
+        return ";".join([",".join(row) for row in all_rows])
+    except Exception:
+        return "error"