fix(test): add @vitest/coverage-v8 dependency for coverage reports

- Add @vitest/coverage-v8@2.1.8 matching vitest version
- Required for test:coverage script to work

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/package.json

@@ -55,6 +55,7 @@
     "@types/react-window": "^2.0.0",
     "@types/uuid": "^10.0.0",
     "@vitejs/plugin-react": "^4.6.0",
+    "@vitest/coverage-v8": "2.1.8",
     "autoprefixer": "^10.4.27",
     "jsdom": "25.0.1",
     "playwright": "^1.58.2",