`RenderPipeline`, SSGI, and the denoise TSL node imported from
`three/webgpu` and `three/tsl` are all WebGPU-only. On a browser
without `navigator.gpu`, the WebGPURenderer falls back to WebGL2, and
attempting to build the TSL post-processing pipeline either throws or
produces broken output — the scene renders for a few frames, then
goes black as the 3-attempt retry loop fights the direct-render
fallback path in `useFrame`.
This sets `hasPipelineErrorRef.current = true` at pipeline setup time
when `navigator.gpu` is undefined, so `useFrame` takes the existing
direct `renderer.render(scene, camera)` path exclusively and never
tries to build the broken TSL pipeline.
No behavioural change in WebGPU mode — the guard only fires when the
WebGPU API is literally not exposed by the browser. The rare edge
case of `navigator.gpu` being defined but device creation failing at
runtime still falls through the existing try/catch unchanged.
