Fix auto device falling back when a provider fails to load

[Suh0161]

Closes #1642

Fix: auto device falls back gracefully when a provider fails to load

When device: 'auto' is used and a high-priority execution provider (e.g. CUDA on Linux without libcuda.so installed) is unavailable, createInferenceSession would throw instead of trying the next provider in the list.

The fallback now lives in constructSessions in session.js, where the device selection context is available. Each provider is tried individually — on failure a warning is logged and the next one is attempted. createInferenceSession itself is unchanged.

// Before: hard crash on Linux x64 without libcuda.so
// After: warns and automatically falls back to the next available provider
await pipeline('text-generation', 'onnx-community/LFM2-1.2B-ONNX', { device: 'auto' });