Refactor: migrate text reader to TypeScript with Yarn 4 build

[carloshskp]

Summary

• migrate the frontend logic into modular TypeScript with a clean TextReaderApp bootstrap and storage/rate utilities
• move static assets into a public folder and add a build pipeline that compiles TypeScript and copies assets with Yarn 4
• replace Vitest setup with Jest and refreshed JSDOM-based tests for responsive rate controls and storage syncing
• update documentation to reflect the new Yarn/Node requirements and static asset locations

Testing

• yarn test
• yarn build

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Codex Task