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.

README.md

@@ -35,7 +35,7 @@ desktop that can be rebuilt from scratch in minutes.
 
 ## Quick Start
 
-### Install
+### Fresh Install (Bare Metal)
 
 1. Boot the [Arch ISO](https://archlinux.org/download/) and download the config:
    ```bash
@@ -53,6 +53,28 @@ The archinstall config clones this repo to `/opt/moonarch` via custom-commands.
 post-install.sh handles the remaining ~100 packages, all configs, themes, services,
 and user setup.
 
+### Transform (Existing Arch+Wayland System)
+
+Already running Arch with a Wayland compositor (Sway, Hyprland, GNOME Wayland, etc.)?
+Transform converts your system to Moonarch without reinstalling.
+
+**Prerequisites:** Active Wayland session, git installed.
+
+```bash
+git clone https://gitea.moonarch.de/nevaforget/moonarch.git /opt/moonarch
+/opt/moonarch/scripts/transform.sh
+```
+
+The script will:
+1. Show a pre-flight summary of all changes
+2. Back up your `~/.config/`, `~/.zshrc`, and `/etc/xdg/` to timestamped tar archives
+3. Disable conflicting display managers (SDDM, GDM, LightDM, etc.)
+4. Remove conflicting packages (e.g. PulseAudio → PipeWire)
+5. Install all Moonarch packages and configs (**hard overwrite** of all user configs)
+6. Enable greetd, firewall, and system services
+
+After completion, **reboot** (do not log out — your previous DM is already disabled).
+
 ### Update
 
 ```bash
@@ -74,7 +96,9 @@ packages/
   aur.txt                       AUR packages (~15), one per line
 
 scripts/
+  lib.sh                        Shared helpers sourced by all scripts
   post-install.sh               Main automation (packages, configs, themes, services)
+  transform.sh                  Convert existing Arch+Wayland system to Moonarch
   install-themes.sh             Cursor theme installer (Sweet-cursors)
   update.sh                     System updater (symlinked to moonarch-update)
 
@@ -113,6 +137,7 @@ defaults/
   shell/zshrc                   Zsh config: prompt, aliases, FZF, completion
   etc/greetd/                   greetd daemon + greeter Niri config
   etc/moongreet/                moongreet configuration
+  user/systemd/user/             Systemd user services (kanshi)
   user/waybar/                  Per-user Waybar overrides (only copied if missing)
   backgrounds/wallpaper.jpg     Default wallpaper (shared by desktop, greeter, lock screen)
 ```
@@ -125,10 +150,12 @@ greetd ─► niri (greeter instance) ─► moongreet ─► user authenticates
                                                          ▼
                                                    niri (user session)
                                                          │
-                           ┌─────────┬──────────┬────────┼────────┬──────────┐
-                           ▼         ▼          ▼        ▼        ▼          ▼
-                        kanshi    waybar      dunst   foot     waypaper   cliphist
-                       (outputs) (bar)    (notify) (server)  (wallpaper) (clipboard)
+                           ┌──────────┬────────┬────────┬──────────┐
+                           ▼          ▼        ▼        ▼          ▼
+                        waybar      dunst   foot     waypaper   cliphist
+                        (bar)    (notify) (server)  (wallpaper) (clipboard)
+
+                        kanshi runs as a systemd user service (graphical-session.target)
 ```
 
 ## Keybinds (Default)
@@ -186,6 +213,12 @@ are part of the system and updated via `moonarch-update`.
 | ufw | Firewall (deny incoming, allow outgoing) |
 | auto-cpufreq | CPU frequency scaling (AC: performance, battery: powersave) |
 
+### User Services (systemd --user)
+
+| Service | Purpose |
+|---------|---------|
+| kanshi | Dynamic display configuration (auto-switch output profiles on hotplug) |
+
 ## Moonarch Ecosystem
 
 Moonarch is the deployment and configuration layer. Three companion projects provide