Enable VirtualBox and add C# Omnisharp support

Update ChatGPT desktop entry icon SHA256 to match new asset.

modules/home/zed/extensions.nix

@@ -21,5 +21,6 @@ _: {
     "opencode"
     "fish"
     "tera"
+    "csharp"
   ];
 }

modules/home/zed/extra-packages.nix

@@ -11,5 +11,6 @@
     deputy
     tailwindcss-language-server
     typescript-language-server
+    omnisharp-roslyn
   ];
 }

modules/home/zed/user-settings/lsp.nix

@@ -153,5 +153,9 @@
         };
       };
     };
+    omnisharp.binary = {
+      path = lib.getExe pkgs.omnisharp-roslyn;
+      arguments = ["-lsp"];
+    };
   };
 }