Compute per-row editability and deletability from a table's row-level
security policies and return them as synthetic columns so clients can
hide edit/delete affordances for rows the user cannot change.
- Introspect pg_policies and relrowsecurity at schema-cache load and
combine the UPDATE/DELETE USING qualifiers per table (permissive OR,
restrictive AND).
- Store the combined qualifiers on Table and inject can_edit/can_delete
as computed select fields when expanding `select *`, only for
RLS-enabled tables with a matching policy (COALESCE'd to a boolean).
- Keep the computed columns out of the OpenAPI spec so they are not
rendered as regular fields.
- Add a cfExpression field to CoercibleField to carry raw SQL
expressions through the planner to SqlFragment.