Invite member

Invites one or more workmates (form field data = JSON {emails: 'a@x,b@y', comment?}). Someone without an account gets Supabase's invitation email and joins on signing in; someone who already has one (a member of other organizations) gets our own email and accepts or declines in the app. Each email gets its own status: sent | resent (was already pending) | already_registered (already in this team) | rate_limited | invalid_email; result is true only when every email was sent.