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/snapper-root.conf

@@ -0,0 +1,37 @@
+# Snapper configuration for the Das OS root file system.
+# das-snapper-setup copies it to /etc/snapper/configs/root.
+
+SUBVOLUME="/"
+FSTYPE="btrfs"
+QGROUP=""
+
+# Snapshots may use at most half of the file system and must leave 20% free.
+SPACE_LIMIT="0.5"
+FREE_LIMIT="0.2"
+
+# Members of wheel can list and compare snapshots without sudo.
+ALLOW_USERS=""
+ALLOW_GROUPS="wheel"
+SYNC_ACL="yes"
+
+BACKGROUND_COMPARISON="yes"
+
+# Snapshots made by das-update and by hand.
+NUMBER_CLEANUP="yes"
+NUMBER_MIN_AGE="3600"
+NUMBER_LIMIT="20"
+NUMBER_LIMIT_IMPORTANT="10"
+
+# Hourly snapshots made by cron.
+TIMELINE_CREATE="yes"
+TIMELINE_CLEANUP="yes"
+TIMELINE_MIN_AGE="3600"
+TIMELINE_LIMIT_HOURLY="5"
+TIMELINE_LIMIT_DAILY="7"
+TIMELINE_LIMIT_WEEKLY="2"
+TIMELINE_LIMIT_MONTHLY="0"
+TIMELINE_LIMIT_QUARTERLY="0"
+TIMELINE_LIMIT_YEARLY="0"
+
+EMPTY_PRE_POST_CLEANUP="yes"
+EMPTY_PRE_POST_MIN_AGE="3600"