Replace Rofi with Walker as application launcher

Walker (GTK4 + Elephant backend) replaces rofi-lbonn-wayland-git as the
central launcher and menu framework.

Native Walker providers replace 5 custom rofi scripts:
- App launcher (desktopapplications provider)
- Clipboard (clipboard provider, replaces cliphist frontend)
- Bluetooth (bluetooth provider, replaces bluetoothctl script)
- Volume/audio (wireplumber provider)
- Sink switcher (wireplumber provider)

3 scripts ported to Walker dmenu mode:
- moonarch-vpn (nmcli)
- moonarch-cpugov (auto-cpufreq)
- moonarch-sink-switcher (pactl)

Settings menu (moonarch-setmen) removed — apps are findable via Walker
app search directly.

Walker theme (gtk-inherit) inherits all colors from the active GTK4
theme instead of hardcoding Catppuccin values.

Walker and Elephant run as systemd user services for instant startup.

Also standardizes GTK theme to Colloid-Grey-Dark-Catppuccin across all
config files (was inconsistent between gsettings and file configs).

Old rofi configs preserved in legacy/rofi/ for reference.

legacy/rofi/bin/moonarch-launcher

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# ABOUTME: Application launcher using rofi with Catppuccin Mocha theme.
+# ABOUTME: Supports window, files, run, and drun modes.
+
+case $1 in
+  window)
+    showmode="window"
+    ;;
+  files)
+    showmode="filebrowser"
+    ;;
+  run)
+    showmode="run"
+    ;;
+  *)
+    showmode="drun"
+    ;;
+esac
+
+## Run
+rofi \
+    -show $showmode \
+    -click-to-exit \
+    -theme /etc/xdg/rofi/themes/launcher.rasi