Create organization invitation

Invite a user to the organization by email. Requires org admin. Behavior:

• If the email maps to an already-confirmed User, attach them as an OrgUser (and to any teamIds) immediately. The response includes a compact invite summary with status accepted and orgId set to the attached org; no invite row is inserted.

• If the email maps to an unconfirmed User with a live pending invite for this org, return the existing invite with status sent. If the existing invite is canceled or expired, reactivate it with status sent.

• Otherwise create the User row (with email_confirmed=false if missing), create a UserInvite row, send the invitation email, and return it with status sent.

Subject to a per-inviter cap of 10 pending invites. Every non-accepted invite within the invite TTL counts toward the cap.