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>

live/branding/issue

@@ -0,0 +1,2 @@
+Das OS \r (\l)
+

live/packages.x86_64

@@ -41,14 +41,19 @@ udisks2
 xdg-user-dirs
 xdg-utils
 
-# System tools for the live medium
+# Boot loader and disk tools, also kept by the installed system
 btrfs-progs
 cryptsetup
 dosfstools
+efibootmgr
 gptfdisk
+grub
+grub-x86_64-efi
 ntfs-3g
+os-prober
 parted
 sudo
+xfsprogs
 
 # Virtual machine guests
 qemu-ga
@@ -56,5 +61,7 @@ spice-vdagent
 virtualbox-ose-guest
 
 # Das OS (local repository)
+das-installer
 das-settings
+das-snapshots
 das-theme