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>

policies/secrets-engine-test.hcl

@@ -0,0 +1,33 @@
+# secrets-engine-test — test/staging stage role policy.
+#
+# Scope: manage approved TEST-stage metadata and values under the test/ prefix,
+# and run positive/negative verification. Cannot touch build/ or prod paths,
+# cannot administer sys/, auth/, or identity/, cannot act as root.
+
+path "secret/data/test/*" {
+  capabilities = ["create", "read", "update", "delete"]
+}
+path "secret/metadata/test/*" {
+  capabilities = ["create", "read", "update", "delete", "list"]
+}
+
+path "sys/policies/acl/se-test-*" {
+  capabilities = ["create", "read", "update", "delete"]
+}
+
+path "auth/approle/role/se-test-*" {
+  capabilities = ["create", "read", "update", "delete"]
+}
+path "auth/approle/role/se-test-*/role-id" {
+  capabilities = ["read"]
+}
+path "auth/approle/role/se-test-*/secret-id" {
+  capabilities = ["create", "update"]
+}
+
+# DENY everything outside the test lane.
+path "secret/data/build/*" { capabilities = ["deny"] }
+path "secret/data/prod/*"  { capabilities = ["deny"] }
+path "sys/*"               { capabilities = ["deny"] }
+path "auth/token/*"        { capabilities = ["deny"] }
+path "identity/*"          { capabilities = ["deny"] }