Constant MIGRATION_UP_STUB 

pub const MIGRATION_UP_STUB: &str = r#"-- Migration: {%name%}
-- Direction: UP
-- Created: {%timestamp%}

-- 在此编写 up SQL
-- CREATE TABLE IF NOT EXISTS {%table_name%} (
--     id BIGINT PRIMARY KEY AUTO_INCREMENT,
--     created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
--     updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
-- );
"#;

迁移 up SQL 模板（对齐 Phinx 风格）