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.

nixos/fuchsia/configuration.nix

@@ -6,7 +6,7 @@
     # Our user configuration and optional user units
     ../common/users/sajenim
     ../common/users/sajenim/steam
-    ../common/users/sajenim/xmonad
+    ../common/users/sajenim/jade
 
     # Optional components
     ../common/optional/yubikey.nix

nixos/fuchsia/services/flatpak/default.nix

@@ -1,10 +1,3 @@
-{pkgs, ...}: {
-  # Required to install flatpak
-  xdg.portal = {
-    enable = true;
-    config.common.default = ["gtk"];
-    extraPortals = [pkgs.xdg-desktop-portal-wlr];
-  };
-
+{...}: {
   services.flatpak.enable = true;
 }