Fix citation year to 2025

Add arXiv citation at end

Remove badges, arXiv tag link, and citation section

Point arXiv badge directly to PDF

Add arXiv/GitHub/AAAI badges and native arXiv tag link

Use official AAAI 2026 citation

Add paper/code links and BibTeX citation

Update README: add YAML frontmatter + reword source/evaluation sections

Add OPERA 1.78M BGE-M3 retrieval corpus (index + meta + README)

initial commit