fix(desktop): green up desktop CI on main

Two breakages surfaced when CI started running desktop tests:

- Root vitest.config.ts replaced default exclude with `["**/.claude/**"]`,
  losing `**/node_modules/**`. Desktop has no local vitest config, so
  vitest scanned into `node_modules/zod/src/v4/classic/tests/*.test.ts`
  and failed on missing peers (`@web-std/file`, `recheck`). Spread
  `configDefaults.exclude` so node_modules stays excluded.

- window-manager dark titlebar color changed from #18181c to #181B1A in
  963c7926 (white-flash fix) but the test was not updated. Update the
  expected color to match the new intended behavior.

vitest.config.ts

@@ -1,6 +1,6 @@
 import fs from "node:fs";
 import path from "node:path";
-import { defineConfig } from "vitest/config";
+import { configDefaults, defineConfig } from "vitest/config";
 
 const appDir = path.resolve(__dirname, "packages/app");
 const appNodeModules = path.resolve(appDir, "node_modules");
@@ -57,6 +57,6 @@ export default defineConfig({
     ],
   },
   test: {
-    exclude: ["**/.claude/**"],
+    exclude: [...configDefaults.exclude, "**/.claude/**"],
   },
 });