feat(cli): add open-reuse validate and register portfolio integrations

Implement Integration Definition validator CLI with schema and index checks,
pytest suite, and CI workflow. Register open-cmis-tck and issue-core-gitea in
the integration index.

Closes OPEN-WP-0003 and OPEN-WP-0004.

AGENTS.md

@@ -156,6 +156,22 @@ get wrong.
 <!-- Append repo-specific agent instructions below this marker.
      The state-hub template sync preserves content after this line. -->
 
+## Integration Registry CLI
+
+Install and validate integration definitions:
+
+```bash
+python -m pip install -e ".[dev]"
+open-reuse validate
+open-reuse validate --repos-base /home/worsch --fail-on-warnings
+pytest -q
+```
+
+- Schema: `schemas/integration.schema.yaml`
+- Index: `registry/indexes/integrations.yaml`
+- Template: `templates/integration-entry.template.yaml`
+- Authoring guide: `registry/README.md`
+
 ---
 
 ## Workplan Convention (ADR-001)