Build a polished, single-file "2048" game as ONE self-contained index.html. HARD CONSTRAINTS (failing any = failing the task): - Exactly one file: index.html. All CSS and JS inline. No build step, no npm, no bundler. It must run by simply opening the file — 100% offline. - No external requests of any kind: no CDN, no <script src=…>, no web fonts, no fetch/XHR, no external images. Use only system fonts and CSS/canvas. GAME REQUIREMENTS: - Classic 4x4 grid. New game starts with two random tiles (value 2 or 4). - Arrow keys AND WASD move tiles. Also support touch swipe on mobile. - Correct merge rules: tiles slide, equal neighbors merge once per move, a tile already formed by a merge this move cannot merge again. Adding a tile only happens if the board actually changed. - After each valid move, spawn one new tile (2 or 4) in a random empty cell. - Score counter (increment by the merged tile's value) AND a "best" score that PERSISTS across reloads via localStorage. - Win detection at 2048 (with a message + option to keep playing) and game-over detection when no move is possible (no empty cell and no adjacent equals). - A "New game" button that fully resets, and smooth CSS animations for tile spawn and movement/merge. - Responsive layout (works down to ~320px wide) and keyboard focus handled so arrow keys work immediately without clicking first. QUALITY BAR: - Tasteful visual design (colored tiles per value, readable numbers, clean spacing) — it should look finished, not a wireframe. - No console errors. No dead buttons. Edge cases handled (rapid key presses, full board, win-then-continue). DEFINITION OF DONE: opening index.html shows a fully playable, good-looking 2048 where merges are correct, best score survives a reload, and win/lose both work.