fix: support Artix and non-systemd installers

[avifenesh]

Summary

• recognize Artix as pacman-based and let unknown distros select an explicit or unambiguous supported package manager
• treat ydotool as an optional fallback when it is unavailable from configured repositories
• skip automatic ydotoold setup without a systemd user manager and print safe per-user supervisor guidance instead
• add fixture-based installer regressions and run them in CI

Why

--force-unknown-distro previously hard-coded the Debian/apt path. The installer also required ydotool and assumed systemd --user, which prevents Artix and other non-systemd systems from completing core setup.

Closes #76.

Validation

• bash -n install.sh scripts/install_sh_test.sh
• scripts/install_sh_test.sh
• cargo fmt --all -- --check
• cargo check --locked --all-targets
• cargo clippy --locked --all-targets -- -D warnings
• cargo test --locked --no-fail-fast
• cargo doc --locked --no-deps --document-private-items
• scripts/mcp_safety_check.py --binary target/debug/computer-use-linux
• npx -y agnix .

Live Artix repository metadata confirms ID=artix without ID_LIKE, and ydotool is currently absent from the official system, world, and galaxy repositories.

Testing needed

This remains a draft because we do not have a real Artix desktop or its user-level init/supervisor setup. Please test ./install.sh and computer-use-linux doctor on that system before this is marked ready.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.