The connection works, but no article came back. That means either the schema is behind the migrations in this repository, or nothing has been seeded. Both are fixed the same way:

npm run build:setup-sql     # bundles every migration into one file
# paste supabase/setup.sql into the SQL editor and run it
npm run seed                # loads the demo articles

If you prefer the CLI, npx supabase db push does the same thing once the project is linked. Create an account under Authentication → Users first — npm run seed promotes the first one to admin so you can reach /admin.