desktops: replace legacy machinery with armbian-config module_desktops

Replace the entire build-time desktop machinery with a single
armbian-config call in the chroot. Desktop packages, branding,
repos, apt pins, and manifests are now owned by configng's
YAML-driven module_desktops pipeline.

Deleted (~10,400 lines):
  config/desktop/         229 files — per-release × per-DE package
                          lists, postinst scripts, appgroups
  artifact-armbian-desktop.sh, artifact-armbian-bsp-desktop.sh
  armbian-desktop-deb.sh, armbian-bsp-desktop-deb.sh
  rootfs-desktop.sh

New build variable DESKTOP_TIER (minimal/mid/full) replaces both
DESKTOP_ENVIRONMENT_CONFIG_NAME and DESKTOP_APPGROUPS_SELECTED.

Interactive DE selection clones configng via fetch_from_repo and
queries the standalone Python parser on the host (no root needed):
  parse_desktop_yaml.py <yaml_dir> --list-json <release> <arch>

Desktop install in distro-agnostic.sh (after armbian-bsp-cli):
  chroot_sdcard "SUDO_USER= DEBIAN_FRONTEND=noninteractive \
    DIALOG=read armbian-config --api module_desktops install \
    de=$DE tier=$TIER mode=build"

mode=build skips user-dependent steps (getuser, group membership,
skel propagation, DM start/autologin) since no real user exists
at image-build time — armbian-firstrun handles those on first boot.

Cleanup across 17 files: artifacts registry, aggregation pipeline,
Python aggregation tools, CLI commands, action.yml, templates,
library-functions.sh source lines, rootfs-create.sh package block,
rootfs cache hash (DESKTOP_TIER replaces deleted vars).

Author: igorpecovnik

action.yml

@@ -185,8 +185,7 @@ runs:
           BUILD_DESKTOP="yes"
           BUILD_MINIMAL="no"
           DESKTOP_ENVIRONMENT="${{ inputs.armbian_ui }}"
-          DESKTOP_APPGROUPS_SELECTED=""
-          DESKTOP_ENVIRONMENT_CONFIG_NAME="config_base"
+          DESKTOP_TIER="mid"
         fi
 
         # go to build folder
@@ -206,8 +205,7 @@ runs:
         BUILD_DESKTOP="${BUILD_DESKTOP}" \
         BUILD_MINIMAL="${BUILD_MINIMAL}" \
         DESKTOP_ENVIRONMENT="${DESKTOP_ENVIRONMENT}" \
-        DESKTOP_APPGROUPS_SELECTED="${DESKTOP_APPGROUPS_SELECTED}" \
-        DESKTOP_ENVIRONMENT_CONFIG_NAME="${DESKTOP_ENVIRONMENT_CONFIG_NAME}" \
+        DESKTOP_TIER="${DESKTOP_TIER}" \
         ENABLE_EXTENSIONS="${{ inputs.armbian_extensions }}" \
         COMPRESS_OUTPUTIMAGE="${{ inputs.armbian_compress }}" \
         SHARE_LOG="yes" \