Function run 

pub async fn run(
    settings: &Settings,
    cluster: Option<String>,
    down: bool,
    dry_run: bool,
) -> Result<(), CliError>

Top-level entry point for mz-deploy dev.

Orchestrates role/privilege validation, dirty-set computation, plan printing, and the drop+create DDL phases.

• cluster — target cluster for every overlay MV and index. Required unless down is set (clap enforces this).
• down — when true, only run the drop phase and exit immediately.
• dry_run — when true, print the plan but issue no DDL.