Implement REUSE-WP-0013 registry establish, update, and stats

Add stats, establish (scaffold, publish-check, discover), and update CLI
commands with optional llm-connect bridge, validate --root for sibling repos,
pytest coverage, and documentation for sibling registry onboarding.

docs/RegistryFederation.md

@@ -97,6 +97,18 @@ curl -fsS "<raw-url>" | head
   source) to an environment variable holding a Bearer token or full header value.
   The hub stores `auth_env` / `auth_header` names only — never secret values.
 
+### Sibling onboarding (CLI)
+
+```bash
+cd ../state-hub
+reuse-surface establish --scaffold --domain helix_forge
+# optional: LLM_CONNECT_URL=... reuse-surface establish --discover --dry-run
+reuse-surface validate --root .
+git push origin main
+reuse-surface establish --publish-check \
+  --raw-url https://gitea.coulomb.social/coulomb/state-hub/raw/main/registry/indexes/capabilities.yaml
+```
+
 ### Registration checklist
 
 1. Merge capability index to the default branch.