feat(vdb): fold in agents/models/fixtures/backup/audit/lockstep
Build-order step 5. Builds on !6 (merged)/!7 (merged)/!8 (merged).
Adds the remaining leaf commands to vdb as subprocess passthroughs — they wrap standalone scripts that own their argparse (check-lockstep/validate-skills run at import + sys.exit), so forwarding verbatim preserves flags, --help, and exit codes. The hot index/serve path stays in-process; only these cold dev/setup tools shell out.
vdb agents -> scripts/generate-agents.py
vdb models -> scripts/detect-models.py
vdb fixtures -> scripts/generate-test-fixtures.py (--vault injected)
vdb backup -> scripts/backup-vault.sh (--vault injected)
vdb audit -> skills/vdb-optimizer/scripts/vault-audit.py (--vault injected)
vdb lockstep -> check-lockstep.py + validate-skills.py (aggregate exit)
Vault-aware wrappers inject --vault <resolved> only when the caller did not pass it. tests/test_vdb_ext.py covers lockstep, the injected wrappers, and the inject/no-inject logic. Full suite green.