Add composable layered world generator V2

[devteapot]

Summary

• Add a deterministic, chunk-addressable layered world generator V2.
• Introduce typed terrain, hydrology, biome, gameplay, edge, spawn, and manifest models.
• Implement composable generation passes, validation, provenance tracking, and serialization.
• Extend the map generator CLI and documentation for layered world generation.

Testing

• Add deterministic generation and validation coverage for 96×96 worlds.
• Add lake connectivity and stable water-body ID checks.
• Verify river connections across chunk boundaries.
• Verify independent edge-pass composition and round-trip serialization.
• Validate chunk completeness for a 256×256 scale fixture.

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