fix: add @types/node to resolve typecheck failures

Vitest globals require @types/node for process.env in test setup.
Tests pass in CI but typecheck fails without it.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

package.json

@@ -29,6 +29,7 @@
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^16.3.2",
     "@testing-library/user-event": "^14.6.1",
+    "@types/node": "^25.6.0",
     "@types/react": "^19.0.6",
     "@types/react-dom": "^19.0.3",
     "@vitejs/plugin-react": "^4.3.4",