Install the `cgg` call-graph CLI on the user's machine. Trigger when the user says "install cgg", "set up cgg", "I don't have cgg", "how do I get cgg", or when another skill (like the `cgg` skill) reports `cgg` is not on PATH and the user wants it installed. Handles bootstrapping Rust via rustup if missing, the C toolchain check that tree-sitter grammars need, choosing between `cargo install cgg` from crates.io (end-user), a `--git` install for unreleased commits, and a clone-based dev install, PATH setup for `~/.cargo/bin`, and a post-install verification. Walks the user through each step rather than running long-running installs without confirmation.
