Add idiomatic documentation to Go, Java, Python, and Rust clients

clients/rust/crates/mxgw-cli/src/main.rs

@@ -1,3 +1,13 @@
+//! `mxgw` — the Rust test CLI for the MXAccess Gateway.
+//!
+//! The binary wraps [`mxgateway_client`] in a `clap`-driven command surface
+//! used by the cross-language smoke matrix and by developers exercising the
+//! gateway by hand. Every subcommand mirrors a single gateway/Galaxy RPC,
+//! prints either a terse line or a JSON document with `--json`, and exits
+//! non-zero on any failure.
+
+#![warn(missing_docs)]
+
 use std::env;
 use std::path::PathBuf;
 use std::process::ExitCode;