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-sink-switcher

@@ -1,11 +1,11 @@
 #!/usr/bin/bash
-# ABOUTME: Rofi-based PulseAudio sink switcher using pactl.
+# ABOUTME: Walker-dmenu PulseAudio sink switcher using pactl.
 # ABOUTME: Changes the default sink and moves all active streams to it.
 
 # choose audio sink via rofi
 # changes default sink and moves all streams to that sink
 
-sink=$(pactl list sinks short | awk '{print $1, $2}' | rofi -dmenu -theme '/etc/xdg/rofi/themes/volume.rasi' -mesg '󱡫 Sink Switcher' -p 'audio sink:' -location 6 -width 100 | awk '{print $1}') &&
+sink=$(pactl list sinks short | awk '{print $1, $2}' | walker -d -p "󱡫 Sink Switcher" | awk '{print $1}') &&
 
 pactl set-default-sink "$sink" &&
 for input in $(pactl list sink-inputs short | awk '{print $1}'); do