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/08-systemd.sh

@@ -9,7 +9,6 @@
 #    - pi-overview.service      : Session dashboard on port 3000
 #    - bw-ssh-keys.service      : Load Bitwarden SSH keys at boot
 #    - mempi-sync.service       : Sync memory DB to Nextcloud
-#    - mempi-sync.timer         : Run mempi-sync on boot +5min
 #    - empty_downloads.service  : Clear Downloads folder at login
 # ===========================================================================
 
@@ -45,7 +44,7 @@ install_service_file "$SERVICES_DIR/pi-overview.service" "pi-overview.service"
 # ---- 4. bw-ssh-keys.service — Load Bitwarden SSH keys at boot ----
 install_service_file "$SERVICES_DIR/bw-ssh-keys.service" "bw-ssh-keys.service"
 
-# ---- 5. mempi-sync.service — Sync memory DB to Nextcloud ----
+# ---- 5. mempi-sync.service + timer — Sync memory DB to Nextcloud ----
 install_service_file "$SERVICES_DIR/mempi-sync.service" "mempi-sync.service"
 
 # ---- 6. empty_downloads.service — Clear Downloads at login ----
@@ -86,7 +85,6 @@ fi
 
 systemctl --user enable --now empty_downloads.service 2>/dev/null && ok "empty_downloads.service enabled" || warn "empty_downloads.service not started."
 
-# (No timers currently)
 
 info "===== Service Status ====="
 systemctl --user list-units --type=service --state=running 2>/dev/null | grep -E "(porridge|swayidle|pi-overview|mempi|bw-ssh|empty)" || true