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/dvpwa-app-init/fixed.py

@@ -0,0 +1,20 @@
+# Provenance: anxolerd/dvpwa init (fixed).
+# repo: anxolerd/dvpwa
+# commit: a1d8f89fac2e57093189853c6527c2b01fc1d9c1
+# parent: a1d8f89fac2e57093189853c6527c2b01fc1d9c1
+# commit_url: https://github.com/anxolerd/dvpwa/blob/a1d8f89fac2e57093189853c6527c2b01fc1d9c1/sqli/app.py#L35
+# cve: 
+# license: MIT
+# function: init
+# relpath: sqli/app.py
+# provenance: human
+# mechanism: permissive_default
+
+    async def get_by_username(conn: Connection, username: str):
+        async with conn.cursor() as cur:
+            await cur.execute(
+                'SELECT id, first_name, middle_name, last_name, '
+                'username, pwd_hash, is_admin FROM users WHERE username = %s',
+                (username,),
+            )
+            return User.from_raw(await cur.fetchone())