Model a Postgres schema with row-level securityPrompt

I'm building {{feature}} on Postgres (Supabase). Users: {{user_roles}}.

Produce a single SQL migration that:
- Creates tables with uuid primary keys, timestamps, foreign keys and check constraints.
- Adds indexes for every foreign key and every column I'll filter or sort by.
- Enables RLS on every table and writes select/insert/update/delete policies per role, using (select auth.uid()).
- Keeps privileged logic in security definer functions with search_path set to ''.

After the SQL, explain each policy in one sentence and list queries I should run to prove a user cannot read another user's rows.