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/calamares/modules/mount.conf

@@ -0,0 +1,48 @@
+---
+extraMounts:
+    - device: proc
+      fs: proc
+      mountPoint: /proc
+    - device: sys
+      fs: sysfs
+      mountPoint: /sys
+    - device: /dev
+      mountPoint: /dev
+      options: [ bind ]
+    - device: tmpfs
+      fs: tmpfs
+      mountPoint: /run
+    - device: /run/udev
+      mountPoint: /run/udev
+      options: [ bind ]
+    - device: efivarfs
+      fs: efivarfs
+      mountPoint: /sys/firmware/efi/efivars
+      efi: true
+
+# The flat layout that snapper-rollback expects: the root in @ and snapshots
+# in @snapshots. Home, logs and the package cache stay out of root snapshots,
+# so a rollback never touches personal files.
+btrfsSubvolumes:
+    - mountPoint: /
+      subvolume: /@
+    - mountPoint: /home
+      subvolume: /@home
+    - mountPoint: /.snapshots
+      subvolume: /@snapshots
+    - mountPoint: /var/log
+      subvolume: /@var_log
+    - mountPoint: /var/cache/xbps
+      subvolume: /@var_cache_xbps
+
+mountOptions:
+    - filesystem: default
+      options: [ defaults ]
+    - filesystem: efi
+      options: [ defaults, umask=0077 ]
+    - filesystem: btrfs
+      options: [ defaults, noatime, compress=zstd:1 ]
+    - filesystem: ext4
+      options: [ defaults, noatime ]
+    - filesystem: xfs
+      options: [ defaults, noatime ]