feat(desktop): setup river window manager.

hosts/ymir/configuration.nix

@@ -104,6 +104,11 @@
   # Enable light for image control
   programs.light.enable = true;
 
+  programs.river = {
+    enable = true;
+    extraPackages = [];
+  };
+
   # Define a user account. Don't forget to set a password with ‘passwd’.
   users.users.crony = {
     isNormalUser = true;