feat(frontend): implement Atari-style Pong game screen

[HMaziviero]

Motivation

• Replace the previous App UI with a small playable Atari-style Pong experience rendered on <canvas> to provide an interactive demo screen.
• Ensure the frontend builds and runs in this environment by adding a missing runtime dependency that caused craco/react-scripts to fail at build/start.
• Provide simple keyboard controls, scoring and win state for quick manual validation.

Description

• Replaced application entry with a new frontend/src/App.js implementing a Pong game loop using requestAnimationFrame, paddle AI, ball physics, collisions, scoring, pause/restart, and keyboard controls (W/S, ↑/↓, Space, R).
• Added dedicated styles in frontend/src/App.css to create an Atari/arcade look (dark background, scoreboard, controls, canvas styling and winner banner).
• Added ajv to frontend/package.json and committed a generated frontend/package-lock.json to resolve module errors encountered when building with craco and react-scripts in this environment.
• Updated repository to include the new files and package lock so local installs/builds are reproducible in CI/local dev shells.

Testing

• Ran npm install --legacy-peer-deps --no-audit --no-fund in frontend and the dependency installation completed successfully.
• Ran npm run build in frontend and the production build completed successfully with a ready build folder.
• Started the dev server with npm start in frontend and it compiled successfully for manual inspection.
• Executed a Playwright check to open http://127.0.0.1:3000 and captured a screenshot of the Pong home screen, which validated the UI rendering.

---

Codex Task