Relocate dist files, fix path references, and misc script improvements

- Move setup_system.conf.dist to system_setup/config.dist/ and
  skel.tar.zst.dist + pack_skel.sh to system_setup/skel/; config/ now
  holds only gitignored local files
- Fix configure.sh CONF_DIST path (was pointing at non-existent
  config/setup_system.conf.dist)
- Fix skel/pack_skel.sh: remove vestigial source line whose path was
  wrong in both old and new location
- Update error messages in setup_system.inc.sh and
  sync_client_software.sh to reference new dist file location
- Move machine_uuid reading/writing into setup_system.inc.sh so all
  scripts have MACHINEID available; setup_system.conf.dist now uses
  MACHINEID conditionally with a hostname fallback
- sync_client_software.sh: fix && / typo (should be && \) that broke
  the flatpak remote-add → install chain; add network error handling
  after flatpak install; cleanup upgrade logic and chown placement
- Update CLAUDE.md and install.md to reflect new dist file locations

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

system_setup/setup_system.inc.sh

@@ -16,6 +16,19 @@
 #    return 0
 #}
 
+#First, get the machine_uuid wich is needed by some userspace programs.
+#As all Parameters that are bound to CPU or Mainboard, are only readable by root, we need to get the values at installtime.
+#On old installations without the file, we will write it whenever possible
+if [ -f $( dirname "$0" )/config.d/machine_uuid.sys ]; then
+    export MACHINEID="$( cat $( dirname "$0" )/config.d/machine_uuid.sys )"
+elif [ "$EUID" -eq 0 ]; then
+    dmidecode -t system | grep -i 'UUID' \
+    | sed 's/UUID: //' | tr '[:upper:]' '[:lower:]' \
+    | sed 's/[^0-9a-z]*//g' | xargs | tail -c 13 \
+    > "$( dirname "$0" )/config.d/machine_uuid.sys"
+    export MACHINEID="$( cat $( dirname "$0" )/config.d/machine_uuid.sys )"
+fi
+
 #Check for configure.conf - used for frist setup of system
 if [[ -f $(dirname "$0")/../config.d/configure.conf ]]; then
     echo "System in configure-mode. Will use $(dirname "$0")/../config.d/configure.conf for setup."
@@ -23,7 +36,7 @@ if [[ -f $(dirname "$0")/../config.d/configure.conf ]]; then
 else
     #Load default system setup file
     if [[ ! -f $(dirname "$0")/../config/setup_system.conf ]]; then
-        echo "System configuration not found. Please make a copy of setup_system.conf.dist, name it setup_system.conf and check the settings in it before running."
+        echo "System configuration not found. Please copy system_setup/config.dist/setup_system.conf.dist to config/setup_system.conf and adjust the settings before running."
         echo "Press any key to continue" && read -n 1 -s -r && exit 1
     fi
     source $(dirname "$0")/../config/setup_system.conf