Super admin sign-in

Full access: post to any university, manage everything. (DIU-only admins use the DIU console.)

Setup (first time): 1) Run supabase/schema.sql in the Supabase SQL Editor. 2) In Authentication → Users, add your admin email + password. 3) Sign in here. Writes are protected by Supabase auth + RLS — the publishable key alone cannot modify data.