单文件 Three.js 第一人称射击游戏：沙漠地图、AI 机器人与狙击镜

Build a browser first-person shooter inspired by a classic competitive bomb-defusal map, as one self-contained HTML file using Three.js with no build step. Create a sandy desert level with tan brick walls, tunnels, a raised catwalk and a long open lane, using PBR materials. Give the player a rifle, a scoped sniper rifle, a submachine gun and a knife, each with firing, reloading and weapon switching. Add around ten AI bots that patrol, react to gunfire and advance on the player's position. Include headshot detection, a kill feed, a health and ammo HUD, a scope overlay and a two-minute round timer. Generate every sound procedurally with the Web Audio API so no audio files are needed. Controls: mouse look, WASD movement, click to fire, R to reload, number keys to switch weapons. Done means the page opens locally and plays a complete round from spawn to the timer ending.