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.

.gitea/workflows/ci.yml

@@ -32,6 +32,9 @@ jobs:
           reuse-surface catalog
           reuse-surface graph --check --fail-on-warnings
 
+      - name: Registry stats (informational)
+        run: reuse-surface stats || true
+
       - name: Planning cohort report (informational)
         run: reuse-surface report cohorts --planning-min D4 || true