Add dynamic parametric building generation - #126

Summary

• Add editable parametric building recipes with presets, validation, stable seeds, and route serialization.
• Integrate buildings into terrain compilation, module composition, streaming, and selection workflows.
• Render cached three-level building LOD meshes with shared materials and deterministic night lighting.
• Update route editor tools, UI, localization, documentation, and example module data.
• Remove gravel road assets and related OSM/import documentation.

Testing

• Added unit tests for building normalization, mesh-key stability, presets, and module composition.
• Not run: full workspace test suite.