Drop explicit gradio pin (HF Space injects gradio[oauth]==sdk_version)

Bump gradio to 5.16.0 (drop client pin to avoid version conflict)

Pin gradio to 5.9.1 + gradio-client to 1.5.4 to fix /api/info crash

Loosen Gradio pin to >=5.0

Initial Space deployment: Stage 2 fusion demo (CPU, free tier)