Stage 4: Calamares installer and Btrfs snapshots (0.2.0)

- Package Calamares 3.4.3 (Qt6, widgets UI) with xbps-src.
- das-installer: Calamares setup for Void/runit with Das OS branding and
  slides. It copies the clean live image (live-base), builds locales and the
  host-only initramfs, rewrites kernels without sparse tails (GRUB 2.12 cannot
  read Btrfs holes at the end of a file), then removes itself.
- das-snapshots: flat Btrfs layout (@, @home, @snapshots, @var_log,
  @var_cache_xbps), snapper with hourly snapshots via cronie, grub-btrfs menu,
  snapper-rollback, and a dracut module that boots read-only snapshots with
  a RAM overlay.
- das-settings 0.2.0: start LightDM with the system locale.
- Live image: GRUB, efibootmgr and the new packages; Das OS /etc/issue.
- Build: wipe stale destdirs before building packages.

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

srcpkgs/das-installer/files/mount-source

@@ -0,0 +1,17 @@
+#!/bin/sh
+# Mount the clean live image for Calamares' unpackfs at /run/das-installer/root.
+#
+# Dracut runs the live root as a device-mapper snapshot (live-rw) that also
+# holds the live user and boot-time tweaks. Its origin, live-base, is the
+# untouched LiveOS/rootfs.img; mount it read-only without journal replay.
+set -eu
+
+root=/run/das-installer/root
+mountpoint -q "$root" && exit 0
+
+if [ ! -b /dev/mapper/live-base ]; then
+	echo "mount-source: /dev/mapper/live-base not found, is this the live system?" >&2
+	exit 1
+fi
+mkdir -p "$root"
+mount -o ro,noload /dev/mapper/live-base "$root"