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/themes/applet.rasi

@@ -0,0 +1,39 @@
+/**
+ * ABOUTME: Shared base theme for simple list applets (clipboard, vpn, cpugov, volume, bluetooth).
+ * ABOUTME: Provides no-icon dmenu layout — individual themes override window size and listview lines.
+ **/
+
+configuration {
+    modi:                       "drun";
+    show-icons:                 false;
+    drun-display-format:        "{name}";
+}
+
+@import                          "../config.rasi"
+@import                          "../colors.rasi"
+
+mainbox {
+    children:                    [ "message", "listview", "inputbar" ];
+}
+
+inputbar {
+    enabled:                     true;
+    children:                    [ "textbox-prompt-colon", "entry", "mode-switcher" ];
+}
+
+listview {
+    enabled:                     true;
+    columns:                     1;
+    lines:                       8;
+    cycle:                       true;
+    dynamic:                     true;
+    scrollbar:                   false;
+    layout:                      vertical;
+    reverse:                     false;
+    fixed-height:                true;
+    fixed-columns:               true;
+}
+
+element-icon {
+    size:                        0px;
+}