onnxruntime hands a webgpu session whatever adapter the browser picks by
default, which on a laptop with both is the one built into the processor: the
export then waits on the slow half of the machine for no reason. The runtime
reads `env.webgpu.powerPreference` when it builds the webgpu session, so set it
to high-performance; a browser with nothing to honour the preference with
still falls back to the threaded wasm path exactly as before.
3dtours
a2c12a2638