Mobile-first sign in for admins, coaches, and parents.
Signup creates a Supabase Auth user and the database trigger creates a matching profile. Team access still requires membership records; signup alone does not grant private team or child access.
Access boundary
Auth proves identity only. Private team data requires `organization_memberships` or `team_memberships` rows.
Parents manage child access through guardian links. Children do not log in.
Admin and coach roles still need an approved membership before privileged actions should appear.