Three separate binaries are replaced by a single `arc` CLI with subcommands:
arc llm prompt/models, arc agent, arc run, arc validate, arc serve
Extract public CLI modules (arc_llm::cli, arc_agent::cli::AgentArgs/run_with_args)
so the new arc-cli crate can dispatch to each library. Integration tests migrate
to crates/arc-cli/tests/cli.rs.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
