feat: Add 3MF export/preview support with custom WASM build

[mikekuniavsky]

Summary

• Enables 3MF export and preview (previously TODO-commented out) using a custom OpenSCAD WASM build with 3MF color support
• Adds readFrom3MFFile.ts using Three.js ThreeMFLoader to render multi-color 3MF previews
• Updates worker to use --export-format=3mf when the file type is 3MF, falling back to binstl otherwise
• Updates Three.js ecosystem packages (@react-three/drei, @react-three/fiber, three) to newer versions
• Fixes Model.tsx to guard against null geometry and enable shadow casting on 3MF meshes
• Adjusts camera FOV and far plane in ThreeJsCanvas.tsx for better large-model visibility

WASM Setup

This PR requires a custom OpenSCAD WASM build with 3MF color support. Since src/vendor/ is gitignored, you must manually download the WASM files before running:

# Download openscad.js and openscad.wasm from:
# https://github.com/mikekuniavsky/openscad-wasm-debug/tree/main/test-server/tests
mkdir -p src/vendor/openscad-wasm
curl -L https://raw.githubusercontent.com/mikekuniavsky/openscad-wasm-debug/main/test-server/tests/openscad.js -o src/vendor/openscad-wasm/openscad.js
curl -L https://raw.githubusercontent.com/mikekuniavsky/openscad-wasm-debug/main/test-server/tests/openscad.wasm -o src/vendor/openscad-wasm/openscad.wasm

Test plan

• Run npm run dev and verify no WASM magic number error in the console
• Render a model and verify STL export still works
• Render a model using color() statements and export as 3MF — verify colors are preserved
• Preview a rendered 3MF file in the viewer — verify multi-color rendering

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