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/pacman/Qi.txt

@@ -288,3 +288,47 @@ Install Date    : Sun Oct  4 00:00:00 2026
 Install Reason  : Installed as a dependency for another package
 Install Script  : No
 Validated By    : Signature
+
+Name            : pfetch
+Version         : 1.10.0-1
+Description     : A pretty system information tool written in POSIX sh.
+Architecture    : any
+URL             : https://github.com/Un1q32/pfetch
+Licenses        : MIT
+Groups          : None
+Provides        : pfetch
+Depends On      : None
+Optional Deps   : None
+Required By     : None
+Optional For    : None
+Conflicts With  : pfetch-git
+Replaces        : None
+Installed Size  : 81.50 KiB
+Packager        : Unknown Packager
+Build Date      : Sat Oct 10 12:42:02 2026
+Install Date    : Sat Oct 10 12:42:04 2026
+Install Reason  : Explicitly installed
+Install Script  : No
+Validated By    : None
+
+Name            : su-dummy-aur
+Version         : 1.0-1
+Description     : Skeptical-updater dummy package AUR (foreign: in no repository)
+Architecture    : any
+URL             : https://example.invalid/su-dummy
+Licenses        : custom
+Groups          : None
+Provides        : None
+Depends On      : None
+Optional Deps   : None
+Required By     : None
+Optional For    : None
+Conflicts With  : None
+Replaces        : None
+Installed Size  : 4.00 B
+Packager        : su-fixture <su-fixture@example.invalid>
+Build Date      : Tue Nov 14 22:13:20 2023
+Install Date    : Fri Oct  9 08:00:00 2026
+Install Reason  : Explicitly installed
+Install Script  : No
+Validated By    : None