Adds a `role` field (admin|member) to user management:
Schema:
- `role TEXT NOT NULL DEFAULT 'member'` added to users table in both
PostgreSQL V14 migration and libSQL schema/incremental migration
- UserRecord gains `role: String` field
- UserIdentity gains `role: String` field, populated from DB in
DbAuthenticator and defaulting to "admin" for single-user mode
Access control:
- AdminUser extractor: returns 403 Forbidden if role != "admin"
- /api/admin/users/* handlers: require AdminUser (create, list,
detail, update, suspend, activate)
- POST /api/invitations: requires AdminUser (only admins can invite)
- User creation accepts optional "role" param (defaults to "member")
- Invitation acceptance creates users with "member" role
Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>
