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-snapshots/files/das-snapper-setup

@@ -0,0 +1,49 @@
+#!/bin/sh
+# Set up snapper for a Das OS root file system on Btrfs.
+#
+# Expects the layout created by the installer: the root in subvolume @ and
+# snapshots in subvolume @snapshots mounted at /.snapshots, which is what
+# snapper-rollback needs. Safe to run again.
+set -eu
+
+msg() { echo "das-snapper-setup: $*"; }
+
+if [ "$(id -u)" -ne 0 ]; then
+	msg "must be run as root" >&2
+	exit 1
+fi
+if [ "$(findmnt -no FSTYPE /)" != btrfs ]; then
+	msg "the root file system is not Btrfs, nothing to do"
+	exit 0
+fi
+if [ "$(findmnt -no FSTYPE /.snapshots 2>/dev/null)" != btrfs ]; then
+	msg "/.snapshots is not a mounted Btrfs subvolume" >&2
+	exit 1
+fi
+
+if [ ! -e /etc/snapper/configs/root ]; then
+	install -m 640 /usr/share/das/snapper/root /etc/snapper/configs/root
+	msg "created /etc/snapper/configs/root"
+fi
+if ! grep -q '^SNAPPER_CONFIGS=".*\broot\b' /etc/conf.d/snapper; then
+	sed -i 's/^SNAPPER_CONFIGS=.*/SNAPPER_CONFIGS="root"/' /etc/conf.d/snapper
+fi
+chmod 750 /.snapshots
+chgrp wheel /.snapshots
+
+# snapper-rollback mounts the top-level subvolume from this device.
+dev=$(findmnt -no SOURCE / | sed 's/\[.*\]$//')
+uuid=$(blkid -s UUID -o value "$dev")
+sed -i "s|^#\?\s*dev = .*|dev = /dev/disk/by-uuid/$uuid|" /etc/snapper-rollback.conf
+
+# Name the GRUB submenu that grub-btrfs adds
+cfg=/etc/default/grub-btrfs/config
+if [ -f "$cfg" ] && ! grep -q '^GRUB_BTRFS_SUBMENUNAME=' "$cfg"; then
+	echo 'GRUB_BTRFS_SUBMENUNAME="Das OS snapshots"' >>"$cfg"
+fi
+
+# Hourly snapshots come from cron, and grub-btrfs adds them to the boot menu.
+for sv in cronie grub-btrfs; do
+	ln -sfn "/etc/sv/$sv" "/etc/runit/runsvdir/default/$sv"
+done
+msg "snapshots are enabled"