feat(geo-layers): port Tile3DLayer mesh content to WebGPU

[ibgreen-openai]

Goal

Port Tile3DLayer's remaining private mesh renderer to WebGPU without changing its WebGL shader path.

This PR is stacked on #10485. Point-cloud tile content already inherits the WebGPU-capable PointCloudLayer; scenegraph tile content is covered separately by #10477.

Changes

• add a focused WGSL shader for Tile3DLayer's internal PBR mesh sublayer
• support normals, UVs, I3S UV regions, per-feature picking IDs, PBR lighting, highlighting, and premultiplied alpha
• add a backend-neutral PBR compatibility module; its WGSL source is ignored on WebGL, while the existing GLSL and dependency behavior is preserved
• avoid isWebGPU branching in shader setup
• expose the WebGPU device tab on the Melbourne point-cloud Tile3DLayer example
• add real WebGPU coverage with and without per-feature IDs/UV regions

The global support-table row remains unchanged until the ScenegraphLayer dependency (#10477) lands.

Validation

• yarn lint (passes; existing repository warnings only)
• yarn test-headless test/modules/geo-layers/mesh-layer.spec.ts test/modules/geo-layers/tile-3d-layer/tile-3d-layer.spec.ts with Chromium WebGPU enabled (2 tests passed)
• commit hooks: 21 node tests passed
• yarn build was attempted and stops in unchanged stacked-base code at modules/core/src/transitions/gpu-interpolation-transition.ts:205 because an existing @ts-expect-error is unused with the local luma 9.4 types

Stack

• Base: feat(mesh-layers): port SimpleMeshLayer to WebGPU #10485 (SimpleMeshLayer WebGPU port)
• Related dependency for scenegraph tile content: feat(mesh-layers): port ScenegraphLayer to WebGPU #10477

[coveralls]

Coverage is 83.095% — codex/webgpu-tile3d-layer into codex/webgpu-simple-mesh-layer. No base build found for codex/webgpu-simple-mesh-layer.