v0.1.0-alpha.3 — Alyx documentation refresh

Documentation presentation update.\n\n- Uses the Alyx neural-rendering comparison as the README hero\n- Removes the less representative previous example asset completely\n- Preserves unstretched aspect-ratio comparisons\n- Retains the one-click ComfyUI runtime setup introduced in alpha.2\n\nAll 7 tests and Comfy Registry validation pass.