fix(desktop): add @testing-library/dom as explicit dev dependency

@testing-library/react@16 declares @testing-library/dom as a peerDependency
and re-exports waitFor/fireEvent/screen/within from it. Without dom installed
as a direct dependency, tsc -b fails with TS2305 in every test file that
imports those names — which breaks the apps/desktop build during installer
bootstrap (Hermes Setup → "INSTALL DIDN'T FINISH").

apps/desktop/package.json

@@ -97,6 +97,7 @@
   },
   "devDependencies": {
     "@eslint/js": "^9.39.4",
+    "@testing-library/dom": "^10.4.0",
     "@testing-library/react": "^16.3.2",
     "@types/hast": "^3.0.4",
     "@types/node": "^24.12.2",