feat: sync mac installer with local shell setup

[dmoliveira]

Summary

• sync the macOS installer with the repo-managed shell, editor, terminal, and helper-script templates
• add support for syncing local config files and helper scripts while keeping optional desktop extras behind --desktop-extras
• document the updated macOS installer behavior, including optional DockDoor, Maccy, Espanso, AppCleaner, borders, yabai, and skhd

Validation

• Lint: cargo clippy --version
• Lint: git diff --check
• Lint: bash -n install_my_programs_mac
• Lint: zsh -n run_commands/my_zshrc
• Test: PATH="/opt/homebrew/bin:$PATH" pre-commit run --files README.md docs/getting-started.md install_my_programs_mac run_commands/codex_config.toml run_commands/my_startship.toml run_commands/my_zshrc
• Test: TOML parse check returned TOML OK
• Test: ./install_my_programs_mac --dry-run