Fix race condition: disable generate during preprocess, use preprocessed image, thread-safe progress

feat: add mouse wheel horizontal scroll to examples gallery, hide scrollbar

feat: replace example images with custom assets and add auto-scrolling marquee

feat: add clear button, SSE progress tracking, multi-session support

UI updates: Pixal3D V1.1 branding, camera settings, readme, ref thumbnail, GPU duration 240s, fix EXR path

gradio server (#3)