Go to supabase.com → New Project → choose a name and password → wait ~1 min for it to provision.

In Supabase → SQL Editor → paste and run:

create table if not exists users (
  id uuid primary key default gen_random_uuid(),
  username text unique not null,
  password_hash text not null,
  role text default 'viewer',
  created_at timestamptz default now()
);
create table if not exists appdata (
  id text primary key,
  data jsonb not null,
  updated_at timestamptz default now()
);
alter table users enable row level security;
alter table appdata enable row level security;
create policy "allow all" on users for all using (true) with check (true);
create policy "allow all" on appdata for all using (true) with check (true);

In Supabase → Project Settings → API → copy Project URL and anon public key.