Enable and query the Neon Data API (PostgREST-compatible REST interface) with JWT auth and RLS

Documented steps

1. Enable: POST /api/v2/projects/{project_id}/branches/{branch_id}/data-api/{database_name} — empty body {}, or {"auth_provider": "neon_auth", "add_default_grants": true} to wire up Neon Auth
2. The 201 response contains the endpoint URL, e.g. https://ep-xxx.apirest.{region}.aws.neon.tech/{db}/rest/v1
3. Grant table access to the JWT-mapped role: GRANT USAGE ON SCHEMA public TO authenticated; GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO authenticated;
4. Enable RLS on every exposed table (ALTER TABLE t ENABLE ROW LEVEL SECURITY) and add policies using auth.user_id(), which reads the JWT 'sub' claim
5. Query PostgREST-style with the JWT: GET {endpoint}/rest/v1/posts?is_published=eq.true with Authorization: Bearer <JWT>; writes use POST/PATCH/DELETE
6. After schema changes, refresh the static schema cache: PATCH /api/v2/projects/{project_id}/branches/{branch_id}/data-api/{database_name}