feat(hooks): Configure Jest and add unit tests for useFetchStories

[wejdenemk]

feat(hooks): add unit tests for useFetchStories; configure Jest (React 19)

• Add comprehensive tests for caching, ETag/304 handling, sorting, and error fallback
• Configure Jest with ts-jest preset and jsdom environment (jest.config.ts)
• Add test setup (jest.setup.ts) with @testing-library/jest-dom and fetch polyfill
• Update package.json with test scripts (test, test:watch)
• Add dev deps: jest, ts-jest, jest-environment-jsdom, @testing-library/react, @testing-library/jest-dom, @types/jest, whatwg-fetch, ts-node

How to run:

• npm i
• npm test -- --coverage

Closes #10