Script claimed to be arch-only in its comment but had no actual guard.
The body always ran, so on debian it tried pacman-key (which doesn't
exist), failed with 'command not found', and aborted the whole bootstrap
chain (run_once_20 and run_onchange_30 never executed).
Fixes:
1. Wrap entire body in {{ if eq .os_family "arch" }} ... {{ end }} so
the script is a no-op on debian (logs a skip message instead of dying)
2. Prepend sudo to pacman-key, pacman -U, pacman -Syu, pacman -S, and
grep /etc/pacman.conf — same user-vs-root pattern that bit run_once_00
chezmoi runs run_once_* scripts as the invoking user (uid != 0).
The earlier check [[ $(id -u) -ne 0 ]] && die ... killed the script
immediately when invoked via 'chezmoi apply' or 'chezmoi init --apply'
from a normal user session.
The scripts use sudo internally for package operations (pacman/apt),
so elevation happens correctly. The id -u check was wrong: it belongs
in a script that's *meant* to be invoked as root directly, not in a
chezmoi-managed script.
