Create a single self-contained file named exactly `index.html` in the current working directory. It must be a small but complete, PLAYABLE browser game: the classic Snake game. Hard requirements (these define \"self-contained\" — follow them exactly): - Everything lives in ONE file, `index.html`: CSS inside a <style> tag, JavaScript inside a <script> tag. - NO build step, NO npm, NO package.json, NO frameworks, NO bundler. - NO external network requests of any kind: no <script src=\"https://...\">, no CDN links, no Google Fonts, no fetch()/XMLHttpRequest, no external images or assets. - It must run correctly by simply opening index.html in a browser, offline. Gameplay requirements: - A visible game board (an HTML <canvas>). - Arrow-key controls to steer the snake. - Food that the snake eats to grow, with a visible score. - Game-over detection (wall or self collision) and a way to restart. Write ONLY the file index.html. Do not create any other files. Do not explain — just build it.