feat(jade): create modular desktop environment

Rename xmonad/ to jade/ and restructure as a complete desktop environment
with hybrid NixOS and home-manager modules. This establishes jade as a
self-contained, gruvbox-themed DE that can eventually be extracted as a flake.

Changes:
- Create jade/ with NixOS module (WM, system packages, GTK theme)
- Create jade/home.nix for home-manager services (wezterm, picom, dunst)
- Move dmenu with gruvbox patches into jade/dmenu/
- Convert wezterm to pure Lua config with gruvbox-material colors
- Move xinitrc into jade/ directory
- Remove feh/scrot from global env (now in jade)
- Remove dmenu overlay from global overlays
- Simplify home-manager desktop features to just user apps

This follows the pattern of real DEs (GNOME, KDE) where system and user
configs are split across NixOS and home-manager modules.

overlays/default.nix

@@ -7,12 +7,7 @@
   # You can change versions, add patches, set compilation flags, anything really.
   # https://nixos.wiki/wiki/Overlays
   modifications = final: prev: {
-    dmenu = prev.dmenu.overrideAttrs (oldAttrs: {
-      patches = [
-        ./patches/dmenu-bar-height-5.2.diff
-        ./patches/dmenu-gruvbox-20210329-9ae8ea5.diff
-      ];
-    });
+    # Currently empty - dmenu patches moved to jade
   };
 
   # When applied, the unstable nixpkgs set (declared in the flake inputs) will