feat(mesh-layers): port ScenegraphLayer to WebGPU

[ibgreen-openai]

Goal

Port ScenegraphLayer to WebGPU while keeping the WebGL path close to master.

This PR is stacked on #10476, which contains only the example data-source fallback. The diff here is limited to WebGPU layer support, device wiring, and support docs.

Changes

• Add WGSL ScenegraphLayer rendering with instance picking, layer opacity, WebGPU depth parameters, and transition guards.
• Add a Scenegraph-specific WebGPU PBR adapter for glTF base-color textures and PBR bindings.
• Keep the existing GLSL flat/PBR selection on WebGL; WebGPU-only paths are gated on the active device.
• Expose device to the image-based-lighting callback and deprecate the legacy gl callback field.
• Enable the website device tabs and pass the selected device through to the example.
• Mark ScenegraphLayer as WebGPU-supported in the docs.

Website example

Example	WebGL2	WebGPU	Notes
ScenegraphLayer	✅	✅	Renders the bundled flight snapshot from #10476; live OpenSky data remains best-effort.

Validation

• yarn build
• yarn lint (passes with existing repository warnings only)
• yarn test-headless test/modules/mesh-layers/scenegraph-layer.spec.ts
• yarn test-website

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Emit instance IDs during WebGPU picking

When a WebGPU picking pass sets picking.isActive, this fragment still returns the shaded material color. Although the vertex shader calculates geometry.pickingColor, it is never carried through FragmentInputs or selected in fragmentMain, unlike the other WGSL layer shaders. Consequently, pickObjectAsync, hover tooltips, and auto-highlighting on a pickable ScenegraphLayer decode arbitrary material RGB values instead of the instance index; pass the picking color as a varying and emit it during picking.

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