Side-by-side browser game at four effort levels

Build a polished, playable browser game from scratch. Create a single-player neon survival game where the player controls a ship inside an arena. Use only vanilla HTML, CSS and JavaScript. Put the complete game in a single index.html file. No external libraries, external assets, CDNs or generated image files. Requirements: -keyboard movement -enemies that spawn and chase the player -shooting -collision detection -health -score -progressively increasing difficulty -game -over state -restart -polished HUD -animations -particle effects -responsive layout -clear controls/instructions The visual design should feel intentional and production-quality, not like a basic demo. You may choose all other implementation and design details yourself. Do not ask me questions. Build it, test it, fix anything you find, and stop when you believe it is ready to ship.