feat(mvp): working secrets-engine CLI for the whynot-design npm publish lane

Implements SECRETS-WP-0002 end to end as a uv-managed Python package:

- catalog: non-secret lane registry + strict validator (build/test/prod)
- stage roles + OpenBao ACL policies; guards refuse wildcards, sys/, identity/,
  admin names, and cross-stage paths before any backend call
- plan/apply: dry-run-first, idempotent policy + approle apply, decision-gated
- decisions: State Hub lookup with local-fixture fallback; non-secret evidence
  to JSONL + hub progress, scrubbed of any value
- provision/verify: mode-0600 file import + generated test values; positive/
  negative checks that never print the value
- exec delivery: `exec --catalog ... -- npm publish` injects the token via a
  temp .npmrc for the child only, cleaned up on exit/failure/interrupt
- ops-warden routing contract + hardening backlog docs
- 34 tests incl. live OpenBao integration; scripts/demo-e2e.sh runs the full
  chain against a throwaway bao dev server

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.decisions/whynot-design-npm-publish.yaml

@@ -0,0 +1,15 @@
+# Local approval fixture for the whynot-design npm publish lane.
+#
+# Stand-in for the canonical State Hub decision object, which does not yet exist
+# (see PRD open question). When a real decision is recorded in State Hub, set the
+# catalog's approval.decision_ref to that decision's UUID and this fixture becomes
+# unnecessary. NON-SECRET: contains no token value.
+id: whynot-design-npm-publish
+title: "Approve whynot-design npm publish lane (prod)"
+status: resolved          # resolved => approved for apply
+superseded_by: null
+decided_by: "Tegwick"
+review_url: ""
+rationale: >-
+  Pilot lane for secrets-engine MVP. Production npm automation token for
+  whynot-design, delivered exec-time only via temporary npm config.