Output EXACTLY ONE complete HTML file. No markdown fences. No explanation before or after the HTML.
The file must run in Chrome with no build step.

Tech stack (required):
- Three.js r170+ from http://cdn.jsdelivr.net
- WebGLRenderer only (NOT WebGPU)
- OrbitControls: orbit a planet at origin; min/max distance clamped

Scene: "Besiege Earth"
- Procedural LOW-POLY planet at origin:
  • Build from icosahedron or cube-sphere (subdivided cube inflated to sphere)
  • Displace vertices with layered simplex/noise for continents and mountains
  • Color by height: deep ocean blue, green lowlands, brown peaks, white ice caps
  • Flat shading (MeshFlatMaterial or computed flat normals) for Besiege-like look
- Thin atmosphere: slightly larger transparent sphere, fresnel/rim glow on edges
- Slow cloud shell: second transparent layer or particle ring, subtle drift
- Surface prop: one medieval SIEGE CATAPULT built from box/cylinder primitives
  (wood brown + metal gray), sitting on land near equator, correctly oriented
  to planet surface normal (not floating, not buried)
- Lighting: warm sun directional + cool ambient; soft gradient sky background
- UI overlay: title "Besiege Earth", subtitle with controls hint
- Animation loop: planet rotates slowly (~0.05 rad/s); optional catapult arm sway
- Responsive full-viewport canvas
- Graceful error message if WebGL unavailable

Constraints:
- All geometry procedural; no external images or models
- Keep total file under 900 lines if possible