feat: add procedural map generation example with MapBuilder library

[cryptochris8]

Summary

Adds a complete procedural map generation example demonstrating how to create voxel maps programmatically using a reusable MapBuilder library.

Includes:

• MapBuilder library with building primitives: fillBox, fillCircle, buildWall, buildStairs, buildPillar, buildHollowBox, and more
• Block texture registry with 181+ validated texture URIs from @hytopia.com/assets
• Sumo Arena generator — circular geometry, tiered amphitheater seating, water moat, pagoda, domed roof
• Floating Islands generator — terrain profiling, procedural trees, ore deposits, bridges, waterfalls
• Server entry point that loads generated maps by environment variable
• README with full API documentation and tutorial for creating custom generators

Based on the MapTopia project. The MapBuilder library eliminates boilerplate when creating procedural maps and validates textures at build time to prevent client crashes from invalid URIs.

Test plan

• Run npm install && npm run build:sumo — generates outputs/sumo-arena.json
• Run npm run build:islands — generates outputs/floating-islands.json
• Run npm run dev:sumo — server starts and loads sumo arena map
• Verify MapBuilder texture validation warns on unknown texture URIs
• Follow README tutorial to create a custom generator

🤖 Generated with Claude Code