Invitation e-mail subsystem - SDK suggestions

1. Expose invitation status on the User entity: Add an "invitation_status" or "is_pending" field to the User entity that reflects whether the user has actually logged in / completed registration after being invited.

2. Separate invitation list endpoint: Provide a base44.users.listInvitations() SDK method (or similar) that returns all pending invitations with metadata (email, role, invited_at, invited_by).

3. Webhook / entity event on user acceptance: Fire an entity event (or automation trigger) when an invited user completes sign-up, so apps can react (e.g., auto-delete a PendingInvite record, send a welcome message).

4. Cancel invitation API: Provide a base44.users.cancelInvitation(email) method so developers do not need to manage cancellation state manually in a separate entity.

5. Allow SendEmail to non-registered users (opt-in): Currently, the Core SendEmail integration silently blocks or rejects emails to addresses that are not registered app users. This prevents apps from sending custom invitation emails, onboarding sequences, or pre-registration communications.

   Suggestion: provide an opt-in flag (e.g. allow_external: true) that permits sending

   to any email address, with appropriate security review / rate limiting.

These additions would eliminate the need for workarounds and make user invitation management a first-class, reliable feature of the platform.