Capture omarchy-air's post-10-16 customizations into its layer

Everything on the Air that existed only on the machine:

- git/config and mimeapps.list, which the omarchy-air-host branch captured
  but profiles never picked up.
- NetBird: netbird-bin under [aur], the networkd drop-in it writes, and a
  setup.sh that runs `netbird service install` and enables the unit (the AUR
  package ships none). `netbird up` stays manual.
- ufw rules beyond Omarchy's stock set and the handoff step's 4242 rule:
  ssh and the ocovo fabric (7746/udp) from the home LAN, 7746 over wt0, and
  7790/tcp.

base gains omarchy-fix-qt-color and a setup.sh that runs it. Qt 6.12's
QtQuick Color singleton shadows the shell's qs.Commons Color, so the bar,
lock screen and polkit dialog lose every colour; the fix renames the
singleton to ShellColor. An omarchy upgrade restores the stock files, so it
is idempotent, skips Qt < 6.12, and no-ops once upstream renames it.
Verified: run against the pristine backup it reproduces the Air's
hand-patched /usr/share/omarchy/shell byte for byte.

Left out on purpose: ocovo-node.service (written by `ocovo service
install`) and environment.d/ohv.conf belong to those projects.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

profiles/machines/macbook-air-m2/packages.txt

@@ -23,6 +23,9 @@ openssh                  # sshd is enabled: the HP reaches it as `ssh air`
 obsidian-appimage        # omarchy-aarch64
 wf-recorder              # screen recording
 
+[aur]
+netbird-bin              # NetBird mesh client; setup.sh installs and enables its service
+
 [optional]
 steam                    # asahi-alarm build, runs x86 games through FEX
 omarchy-steam-fex