chore(wp-0001): close State Hub bootstrap workplan; de-template repo identity

- repo-identity.md / repo-boundary.md: replace leftover repo-seed template text
  with secrets-engine identity and boundary (T01)
- mark SECRETS-WP-0001 T01–T03 done (T02 dev-workflow commands and T03 first real
  workplan were completed during the MVP build); workplan status -> finished

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

.claude/rules/repo-boundary.md

@@ -1,8 +1,12 @@
 ## Repo boundary
 
-This repo owns **Repo Seed** only. It does not own:
+This repo owns the **secrets-engine** workflow/interaction layer only. It does
+not own:
 
-<!-- TODO: List what belongs in adjacent repos, e.g.:
-- SSH key management → railiance-infra/
-- State hub code     → state-hub/
--->
+- Secret custody, policy, lease, and audit backend → OpenBao / railiance-platform
+- SSH certificate issuance → ops-warden (`warden sign`)
+- Tunnels and remote transport → ops-bridge
+- Authorization decisions → flex-auth
+- Identity and claim lifecycle → user-engine / key-cape
+- Cross-system security boundary doc → net-kingdom/docs/
+- Request history and progress index → State Hub (read model)

.claude/rules/repo-identity.md

@@ -1,5 +1,7 @@
-**Purpose:** Git repository template to bootstrap coulomb projects.
+**Purpose:** OpenBao-backed secrets workflow and automation layer for approved
+secret custody, delivery, and lifecycle work across build, test, and production.
 
 **Domain:** infotech
-**Repo slug:** repo-seed
+**Repo slug:** secrets-engine
 **Topic ID:** cee7bedf-2b48-46ef-8601-006474f2ad7a
+**Workplan prefix:** SECRETS-WP-