Add mirrorlist and pacman.conf to live airootfs

Without these the live system has no mirrors configured and pacman
refuses to sync. Uses geo.mirror.pkgbuild.com as primary with
kernel.org, rackspace, and MIT as fallbacks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/profile/airootfs/etc/pacman.conf

@@ -0,0 +1,16 @@
+[options]
+HoldPkg      = pacman glibc
+Architecture = auto
+CheckSpace
+ParallelDownloads = 5
+SigLevel     = Required DatabaseOptional
+LocalFileSigLevel = Optional
+
+[core]
+Include = /etc/pacman.d/mirrorlist
+
+[extra]
+Include = /etc/pacman.d/mirrorlist
+
+[multilib]
+Include = /etc/pacman.d/mirrorlist

iso/profile/airootfs/etc/pacman.d/mirrorlist

@@ -0,0 +1,4 @@
+Server = https://geo.mirror.pkgbuild.com/$repo/os/$arch
+Server = https://mirrors.kernel.org/archlinux/$repo/os/$arch
+Server = https://mirror.rackspace.com/archlinux/$repo/os/$arch
+Server = https://mirrors.mit.edu/archlinux/$repo/os/$arch