Add transform script for existing Arch+Wayland systems

Extract shared helpers into lib.sh (log, err, confirm, path constants)
and refactor post-install.sh + update.sh to source it.

New transform.sh converts an existing Arch+Wayland system to Moonarch:
pre-flight summary, config backup, DM conflict resolution, PulseAudio
removal, full package install, and hard overwrite of all configs.

Also migrate kanshi from niri spawn-at-startup to systemd user service.

scripts/post-install.sh

@@ -4,37 +4,12 @@
 
 set -euo pipefail
 
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
-OFFICIAL_PACKAGES="$PROJECT_DIR/packages/official.txt"
-AUR_PACKAGES="$PROJECT_DIR/packages/aur.txt"
-DEFAULTS_DIR="$PROJECT_DIR/defaults"
-
-# --- Helper functions ---
-
-log() {
-    echo -e "\e[1;34m[Moonarch]\e[0m $*"
-}
-
-err() {
-    echo -e "\e[1;31m[Moonarch ERROR]\e[0m $*" >&2
-}
-
-read_packages() {
-    grep -v '^\s*#' "$1" | grep -v '^\s*$'
-}
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/lib.sh"
 
 # --- Prerequisites ---
 
-if [[ $EUID -eq 0 ]]; then
-    err "Do NOT run as root. The script uses sudo where needed."
-    exit 1
-fi
-
-if ! command -v pacman &>/dev/null; then
-    err "pacman not found — is this really Arch Linux?"
-    exit 1
-fi
+check_not_root
+check_pacman
 
 # --- Install official packages ---
 
@@ -251,6 +226,22 @@ if [[ -d "$USER_DEFAULTS_DIR" ]]; then
     done
 fi
 
+# --- Enable systemd user services ---
+
+log "Enabling systemd user services..."
+USER_SERVICES=(
+    "kanshi"
+)
+
+for service in "${USER_SERVICES[@]}"; do
+    if systemctl --user list-unit-files "${service}.service" &>/dev/null; then
+        systemctl --user enable "$service"
+        log "  + $service (user)"
+    else
+        log "  ~ $service (user) not found, skipped."
+    fi
+done
+
 # --- Screenshots directory ---
 
 mkdir -p "$HOME/Pictures/Screenshots"