feat: Add AeThex cross-platform avatar toolkit
Implement comprehensive avatar import/export/rigging system supporting:
- Roblox (R6, R15, Rthro), VRChat, RecRoom, Spatial, Sandbox
- Decentraland, Meta Horizon, NeosVR, Resonite, ChilloutVR
- Universal AeThex format for lossless cross-platform conversion
Features:
- Platform-specific skeleton specs and bone mappings
- Auto-rig detection and universal bone name resolution
- Format handlers for GLB, GLTF, FBX, VRM, OBJ, PMX
- Validation against platform constraints (polygons, bones, textures)
- Avatar templates and optimization presets
- Compatibility scoring between platforms