nixos: add quickshell/waybar/taffybar modules

- Switch taffybar input to the local submodule
- Add caelestia quickshell (home-manager module)
- Make waybar/taffybar mutually exclusive, defaulting based on xmonad
- Move tray ordering and status notifier watcher config into the right modules

nixos/desktop.nix

@@ -1,4 +1,4 @@
-{ inputs, config, pkgs, makeEnable, ... }:
+{ inputs, config, pkgs, lib, makeEnable, ... }:
 makeEnable config "myModules.desktop" true {
   services.greenclip.enable = true;
   imports = [
@@ -8,6 +8,16 @@ makeEnable config "myModules.desktop" true {
     ./xremap.nix
   ];
 
+  assertions = [
+    {
+      assertion = config.myModules.taffybar.enable != config.myModules.waybar.enable;
+      message = "Enable exactly one of myModules.taffybar or myModules.waybar.";
+    }
+  ];
+
+  myModules.taffybar.enable = lib.mkDefault config.myModules.xmonad.enable;
+  myModules.waybar.enable = lib.mkDefault (!config.myModules.xmonad.enable);
+
   services.xserver = {
     exportConfiguration = true;
     enable = true;