Add PUT /admin/api/groups/:id/rename (owner role) which re-points the group's routes, migrates the per-group webhook secret (tenant:{id}) and pending invites, and records an audit entry. The group editor's id field is now editable and the console renames first, then persists remaining edits under the new id.
Cloudflare KV's list operation is eventually consistent and can lag
behind a fresh write, so pending invites were invisible right after
creation (GET /admin/api/groups/:id/invites returned {invites: []}).
Keep a per-group token index (invite:group:{id}) updated on create,
revoke, accept and expiry; the members panel also inserts the freshly
created invite into the list immediately and copies the absolute link.
