fix: add @types/jest so ForkTsCheckerWebpackPlugin sees jest globals

The tsconfig declares "types": ["jest"] but @types/jest was not
installed, so TypeScript treated jest as a namespace rather than a
value.  Adding the matching type definitions lets the webpack
type-checker process test files without errors.

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

Author: arbrandes

package-lock.json

@@ -58,6 +58,7 @@
     "@testing-library/jest-dom": "^6.6.3",
     "@testing-library/react": "^16.3.0",
     "@testing-library/user-event": "^14.6.1",
+    "@types/jest": "^29.5.14",
     "identity-obj-proxy": "^3.0.0",
     "jest": "^29.7.0",
     "jest-environment-jsdom": "^29.7.0",