feat(aur): list and upgrade AUR packages through paru or yay on Arch

On the pacman backend, an installed AUR helper (paru, else yay;
--aur-helper=paru|yay|none, --no-aur) adds the AUR updates to the review
list. The helper never runs as root: when the tool is root through sudo it
runs as SUDO_USER (runuser -u, else sudo -u, with that user's HOME, from
that home); unprivileged it runs as is; a root login gets no AUR, with a
warning. The banner names the helper ("+ AUR via paru").

- listing: <helper> -Qua (also with --no-refresh), rows with repository
  "aur"; [ignored] is shown [held]; a failing -Qua warns and the session
  goes on with the repository rows
- every row has a marker column after the number: "*" for AUR rows, a
  space otherwise (on every backend)
- N?? merges pacman -Qi with <helper> -Sia; N?, N+, Nx stay with pacman;
  N- excludes through the helper's --ignore
- <enter>: the repository step exactly as before, then <helper> -Sua
  --ignore <excluded> as the invoking user (--noconfirm only when stdin is
  not a terminal); pacman is skipped when only AUR rows are left; a helper
  failure is reported and its status returned; --dry-run prints it
- other backends never run a helper; --aur-helper is ignored with a warning

paru 2.1.0 and yay 13.0.1 formats verified in discovery/pacman.md section
15 (proof: discovery/pacman/aur.sh). Unit tests replay the recorded output
(fake paru, yay, runuser, getent); the archlinux E2E run installs the
foreign su-dummy-aur and drives a fake paru through a fake sudo built on
passwordless su for wheel.

tests/unit/data/aur/Sia-yay-pfetch.txt

@@ -0,0 +1,23 @@
+Repository                    : aur
+Name                          : pfetch
+Version                       : 1.11.0-1
+Description                   : A pretty system information tool written in POSIX sh.
+URL                           : https://github.com/Un1q32/pfetch
+Licenses                      : MIT
+Groups                        : None
+Provides                      : pfetch
+Depends On                    : None
+Optional Deps                 : None
+Make Deps                     : None
+Check Deps                    : None
+Conflicts With                : pfetch-git
+Replaces                      : None
+AUR URL                       : https://aur.archlinux.org/packages/pfetch
+First Submitted               : Sat 16 Jan 2021 09:13:08 AM UTC
+Keywords                      : fetch
+Last Modified                 : Tue 09 Jun 2026 10:43:50 PM UTC
+Maintainer                    : yigits
+Popularity                    : 0.103440
+Votes                         : 48
+Out-of-date                   : No
+