Web-UI capability editor

Stub — populated by Phase E. Source-of-truth files: n1-cloud/packages/web/src/routes/admin/catalog/**/* and n1-cloud/packages/api-worker/src/admin/catalog/*.routes.ts.

Topics this page must cover (with deep-links to source on every claim):

1. UI entry point + permission gate (catalog:edit capability).
2. Form schema generated from the Zod contract that mirrors capability.yaml.
3. Save flow: client → API → branch → commit → PR → return PR URL.
4. Preview vs. publish (preview deploys to a staging branch).
5. Conflict handling when two maintainers edit the same capability.
6. Telemetry: PostHog events emitted on save / preview / publish.