Castle Above Clouds Real-Time 3D Experience

You are an expert creative developer specializing in real-time 3D web graphics, combining technical precision with artistic vision.

# Task
Build a complete, production-ready Three.js web experience showcasing physically-based rendering (PBR) in a single HTML file. The scene must be performant, visually striking, and tell a cohesive atmospheric story.

# Scene Requirements
**Title Card (HTML overlay)**
- Main title: "CASTLE ABOVE CLOUDS" (bold, architectural serif or strong sans, 48–72px)
- Subtitle lockup: "A DREAM IN THE SKY · REBUILT" (light weight, letterspaced, 14–18px)
- Hero line: "Above the" (mixed weights: "Above" regular 120px, "the" light 120px)
- Fade in on load, fade out after 3 seconds

**3D Scene**
- Central subject: {{scene-description}}
- Environment: Volumetric clouds below and around the subject, dynamic sky gradient (dawn/dusk palette), god rays or atmospheric scattering
- Camera: Slow orbital movement or gentle floating motion that reveals scale and detail
- Lighting: HDRI environment map or three-point setup (key, fill, rim) optimized for PBR
- Materials: Use MeshStandardMaterial or MeshPhysicalMaterial with proper roughness, metalness, and normal maps where appropriate
- Performance target: 60 FPS on modern desktop browsers

# Technical Specifications
- **Single self-contained HTML file** with embedded CSS and JavaScript
- Three.js via CDN (r150 or newer)
- Responsive canvas (100vw × 100vh)
- OrbitControls or gentle automated camera path
- Anti-aliasing enabled
- No external asset dependencies—use procedural geometry (BoxGeometry, CylinderGeometry, etc.) and code-generated textures/materials
- Clean, commented code structure: setup → scene/camera/renderer → geometry → materials → lighting → animation loop

# Artistic Direction
- Mood: {{mood}}
- Color palette: Harmonious with the "dream in the sky" theme—think ethereal blues, warm gold highlights, soft purples, or your interpreted palette matching the mood
- Clouds: Use instanced geometry or particle systems for performance; consider additive blending for glow
- Scale: Convey vastness—small architectural details against enormous sky

# Code Quality
- Modular functions (initScene, createClouds, animateCamera, etc.)
- Dispose of geometries/materials properly if recreating
- Graceful fallback message if WebGL is unavailable
- Include a subtle loading indicator or progress note in the title card

# Deliverable
Output the complete HTML file ready to save and open in a browser. Begin with `<!DOCTYPE html>` and end with `</html>`. Include brief inline comments explaining PBR material choices, lighting rationale, and any performance optimizations.