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-setmen

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# ABOUTME: Walker-dmenu settings menu that lists desktop files from /usr/share/settings-menu/.
+# ABOUTME: Reads Name and Icon from .desktop files and launches the selected entry.
+
+SETTINGS_DIR="/usr/share/settings-menu"
+
+declare -A EXEC_MAP
+
+get_name() {
+    local lang
+    lang=$(locale | grep "^LANG=" | cut -d= -f2 | cut -d_ -f1)
+    local find="Name[$lang]="
+    local name
+
+    name=$(grep "^$find" "$1" | tail -1 | sed "s/^$find//" | sed 's/%.//' | sed 's/^"//g' | sed 's/" *$//g')
+
+    if [[ -z "$name" ]]; then
+        name=$(grep "^Name=" "$1" | tail -1 | sed 's/^Name=//' | sed 's/%.//' | sed 's/^"//g' | sed 's/" *$//g')
+    fi
+
+    echo "$name"
+}
+
+get_exec() {
+    grep '^Exec=' "$1" | tail -1 | sed 's/^Exec=//' | sed 's/%.//' | sed 's/^"//g' | sed 's/" *$//g'
+}
+
+entries=""
+for file in "$SETTINGS_DIR"/*.desktop; do
+    [[ -f "$file" ]] || continue
+    name=$(get_name "$file")
+    [[ -z "$name" ]] && continue
+    EXEC_MAP["$name"]=$(get_exec "$file")
+    entries+="$name\n"
+done
+
+chosen=$(echo -e "$entries" | sed '/^$/d' | sort | walker -d -p "⚙  Settings")
+
+if [[ -n "$chosen" && -n "${EXEC_MAP[$chosen]}" ]]; then
+    ${EXEC_MAP[$chosen]} &disown
+fi