Build a first-person zombie slasher prototype in Three.js

Submit exactly one file named `index.html`. All custom HTML, CSS, and JavaScript must be contained inside this single file. Three.js may be loaded from a reliable public CDN, but there must be no additional project files, asset folders, package installation, or build step. The submitted file must run in a modern desktop browser when opened or served from a basic local static server.

- First-person movement using WASD - Mouse-controlled camera using pointer lock - A visible melee weapon - Attack using left mouse click - A clear weapon swing or attack animation - Zombie enemies that move toward and attack the player - Working collision and attack-distance checks - Zombies must take damage and be killable - Player health - Kill or score counter - Additional zombies must spawn so the game continues after the first kill - Game-over state when the player loses all health - A working restart button or restart key - Start screen displaying the controls VISUAL AND TECHNICAL REQUIREMENTS - Use Three.js for the 3D scene and gameplay - Create a coherent arena with lighting, ground, boundaries, and atmosphere - Use procedural geometry, CSS, data URLs, or other content embedded in the HTML - Do not depend on external models, textures, audio files, or asset folders - Avoid graphic gore; stylized zombie violence is sufficient - The page must not display missing assets or unresolved loading errors - Gameplay should remain usable at a normal desktop screen size

- WASD: move - Mouse: look - Left click: attack - R: restart after game over - Escape: release mouse

The submission will be accepted if: 1. It consists of one working `index.html` file. 2. It loads without fatal console errors. 3. No build process or package installation is required. 4. The player can start the game, move, look around, and attack. 5. Zombies visibly approach the player and can damage them. 6. The player can kill zombies using the melee weapon. 7. Health, kills, game over, and restart all function. 8. The result feels like a coherent playable prototype rather than a static scene or controls demonstration. Please test the final HTML before submitting it.