fix: add back HF Spaces YAML frontmatter

docs: professional redesign of README.md with badges and improved layout

docs: professional redesign of README.md

docs: update README with demo link and documentation info

chore: update Gradio to 6.12.0 and fix HF Spaces compatibility

feat: update XGBoost weights URL and add Gradio demo

docs: add project README, CONTRIBUTING guide, and per-package READMEs

chore: bootstrap pdfsys workspace with 7 package skeletons