Simplify and clean up provisioning scripts

- lib/distro.sh: add DISTRO_CODENAME from VERSION_CODENAME; remove
  unused REPO_ADD_RPM variable; export DISTRO_CODENAME

- stages/01-repos.sh: replace repeated '. /etc/os-release' subshell
  calls with $DISTRO_CODENAME in Docker and Tailscale repo lines

- stages/00-envcheck.sh: combine four mkdir -p calls into one

- stages/02-packages.sh: remove identical if/else branches in fd
  symlink block; both branches were the same command

- stages/03-toolchains.sh: set NVM_DIR once before the if/else instead
  of twice; remove dead commented-out duplicate curl line

- stages/04-shell.sh: capture $(date +%Y%m%d) into _bak_date once per
  backup and reuse in cp and warn to avoid redundant forks

- stages/06-scripts.sh: split 'export VAR=$(cmd)' into assignment +
  export to correctly propagate errors under set -euo pipefail

- stages/07-uv-projects.sh: remove unused has_package_json field (always
  false, never read); fix stage completion message 06 -> 07

- stages/08-systemd.sh: remove mempi-sync.timer (deploy, enable, header
  comment); deploy mempi-sync.service only

- stages/09-desktop.sh: remove duplicate mkdir -p in COSMIC section;
  remove unused repo_url parameter from install_nerd_font()

- stages/12-other-apps.sh: replace manual distro branch for Nextcloud
  with pkg_install_mapped

- config/scripts/bw-load-ssh.sh: split 'export BW_SESSION=$(cat ...)'
  into assignment + export

- config/systemd/mempi-sync.timer: delete file

stages/09-desktop.sh

@@ -98,7 +98,6 @@ case "$DE" in
       cp "$CONFIG_DIR/cosmic/custom-shortcuts.ron" \
         "$HOME/.config/cosmic/com.system76.CosmicSettings.Shortcuts/v1/custom"
       # Set terminal command (COSMIC desktop)
-      mkdir -p "$HOME/.config/cosmic/com.system76.CosmicSettings.Shortcuts/v1"
       echo '{
     Terminal: "/usr/bin/ghostty --gtk-single-instance=true",
 }' > "$HOME/.config/cosmic/com.system76.CosmicSettings.Shortcuts/v1/system_actions"
@@ -187,7 +186,6 @@ mkdir -p "$FONT_DIR"
 # This is the font used on the Pop machine (MesloLGS NF Regular).
 install_nerd_font() {
   local font_name="$1"
-  local repo_url="$2"
   local font_dir="$FONT_DIR"
 
   # Check if already installed
@@ -213,8 +211,8 @@ install_nerd_font() {
 # MesloLGS NF (Regular, Bold, Italic, Bold Italic)
 # FiraCode Nerd Font Propo
 # ApercuMonoPro-Regular.otf (proprietary — not distributed)
-install_nerd_font "Meslo" ""
-install_nerd_font "FiraCode" ""
+install_nerd_font "Meslo"
+install_nerd_font "FiraCode"
 
 # Rebuild font cache
 fc-cache -f "$FONT_DIR" 2>/dev/null || true