PimSim: Unreal-to-splat and cooked-physics pipeline

[dimos-bot]

Turn one versioned Unreal-class scene into aligned camera and physical worlds.

Acceptance

• Preserve asset hierarchy, IDs, transforms, materials, and available semantics
• Export deterministic RGB, masks, depth, intrinsics, and extrinsics
• Run COLMAP mapping, densification, and splat training with retained provenance
• Cook source geometry independently into collision, navigation, and MuJoCo assets
• Measure alignment and run ordinary DimOS camera and navigation workflows

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Synced from DIM-1383