Stage 6: server image with a console installer (0.4.0)

- server/ profile and build-iso.sh [desktop|server]; make iso-server,
  make qemu-server, run-qemu.sh --serial; login on tty and ttyS0
- das-server: SSH, chrony, NetworkManager/dhcpcd, Docker with Compose,
  nftables (closed except SSH, own table), fail2ban reading socklog,
  sshd without root passwords, Docker log rotation, tools
- das-server-install: dialog installer in Ukrainian and English, or
  unattended with --config; GPT + Btrfs subvolumes, GRUB for UEFI and BIOS,
  serial console, SSH key with optional keys-only logins
- das-install-common: mount-source and postinstall shared with Calamares
- dsv: runit service manager (list, enable, disable, start, stop,
  restart, status, logs) with bash completion, also on the desktop
- das-update split into a subpackage without GTK; the window and tray
  icon move to /usr/libexec/das/das-update-gui
- das-snapper-setup enables dbus, which snapper needs
- TODO: ISO size review with measured numbers and options

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/container/build-packages.sh

@@ -41,6 +41,11 @@ for dir in /work/srcpkgs/*/; do
     echo "warning: $name is now in void-packages, consider dropping our template" >&2
   fi
   rm -rf "$vp/srcpkgs/$name"
+  # A subpackage is a link to its source package's directory and is built with it
+  if [[ -L ${dir%/} ]]; then
+    as_builder ln -s "$(readlink "${dir%/}")" "$vp/srcpkgs/$name"
+    continue
+  fi
   as_builder cp -rL "$dir" "$vp/srcpkgs/$name"
   names+=("$name")
 done