//! App entry point for the `apimock` executable.
//!
//! # Why `anyhow::Result` here
//!
//! Internal code uses the typed `AppError` from `core::error`. At the
//! process boundary we only care about printing a single human-readable
//! line and exiting non-zero, so we flatten into `anyhow::Result` — this
//! gives a free `Display` via `?` in `main` without any ceremony.
async