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.

packages/aur.txt

@@ -9,7 +9,17 @@ colloid-catppuccin-gtk-theme-git
 colloid-catppuccin-theme-git
 
 # Niri / Wayland Extras
-rofi-lbonn-wayland-git
+walker-bin
+elephant-bin
+elephant-desktopapplications-bin
+elephant-clipboard-bin
+elephant-bluetooth-bin
+elephant-calc-bin
+elephant-runner-bin
+elephant-files-bin
+elephant-providerlist-bin
+elephant-niriactions-bin
+elephant-wireplumber-bin
 waybar-niri-windows-bin
 waybar-niri-workspaces-enhanced-git
 waypaper