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.

defaults/bin/moonarch-cpugov

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# ABOUTME: Rofi-based CPU governor switcher using auto-cpufreq.
+# ABOUTME: Walker-dmenu CPU governor switcher using auto-cpufreq.
 # ABOUTME: Allows switching between performance, powersave, and reset modes.
 
 declare -A LABELS
@@ -38,8 +38,7 @@ function print_menu()
 ##
 function start()
 {
-    # print_menu | rofi -dmenu -p "?=>"
-    print_menu | sort | rofi -theme /etc/xdg/rofi/themes/cpugov.rasi -show "CPU Modes" -dmenu -mesg "󰓅  CPU Modes" -i -p "rofi-bangs: "
+    print_menu | sort | walker -d -p "󰓅  CPU Mode"
 }
 
 
@@ -66,5 +65,5 @@ then
 
     notify-send -h string:x-canonical-private-synchronous:cpugov -i cpu "CPU Mode" "Set to $choice ${LABELS[$choice]}"
 else
-    echo "Unknown command: ${choice}" | rofi -dmenu -p "error"
+    notify-send -u critical "CPU Governor" "Unknown command: ${choice}"
 fi