Schema DDL from declared columns: Model::create_table_sql (SQLite affinities) and
create_table_sql_for for PostgreSQL and MySQL, covering autoincrement idioms
(AUTOINCREMENT / SERIAL / AUTO_INCREMENT), UNIQUE, DEFAULT, column CHECK,
foreign keys with ON DELETE/ON UPDATE, and a composite primary key rendered as a
table-level constraint. Also a lone Column::ddl, ColumnType::sql_for across
dialects, and index_ddl. All identifiers are trusted, declared in code — never bound.
moon run examples/10-schema-ddl