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>

scripts/container/build-packages.sh

@@ -50,6 +50,9 @@ cd "$vp"
 if [[ ! -f masterdir-x86_64/.xbps_chroot_init ]]; then
   as_builder ./xbps-src -H "$hostdir" binary-bootstrap
 fi
+# A failed build leaves its destdir behind, and the next build of that package
+# (also as a dependency of another one) would package the stale files
+rm -rf masterdir-x86_64/destdir/*
 for name in "${names[@]}"; do
   echo "==> Building $name"
   as_builder ./xbps-src -H "$hostdir" -f pkg "$name"