fix(design-system): add @storybook/test and @testing-library/dom deps

- @storybook/test needed by stories (import { fn })
- npm overrides resolves peer dep conflict with storybook 10
- @testing-library/dom explicit dep (peer of @testing-library/react)
- 157 design-system tests + 111 frontend tests all pass

package.json

@@ -38,5 +38,10 @@
     "husky": "^9.1.7",
     "lint-staged": "^16.4.0",
     "prettier": "^3.0.0"
+  },
+  "overrides": {
+    "@storybook/test": {
+      "storybook": "10.4.6"
+    }
   }
 }

packages/design-system/package.json

@@ -30,6 +30,8 @@
     "@storybook/addon-a11y": "^10.2.9",
     "@storybook/addon-vitest": "^10.2.9",
     "@storybook/react-vite": "^10.2.9",
+    "@storybook/test": "^8.6.0",
+    "@testing-library/dom": "^10.4.0",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^16.3.2",
     "@testing-library/user-event": "^14.6.1",