Build Rust CLI Project

Purpose

Implement Rust command-line behavior with a clear boundary between user input, command execution, domain logic, and output.

The practical goal is a CLI that is easy to test, has descriptive operator-facing messages, and validates with the repository's Cargo commands.

Source Check

Use official Rust and Cargo documentation first:

• The Rust Programming Language
• The Cargo Book
• Cargo package layout
• Cargo tests guide
• std::process::ExitCode
• std::env::args