Improve academic website content and structure

[jinlx]

Summary

• add Lixu Jin's verified Google Scholar profile and recent homepage highlights
• strengthen the Research page with related papers, datasets, code, and presentations
• rename the Research URL to /research/ while preserving /researches/ as a redirect
• simplify the sidebar, footer, and web CV presentation
• remove unused sample pages, comments, author data, and demo images

Why

These changes make the website easier to scan, better connect research outputs, and reduce unused template content that made the repository harder to maintain.

Validation

• parsed the site YAML configuration and navigation data
• verified referenced local images and downloadable files
• checked the committed diff for whitespace errors
• confirmed the Google Scholar URL and Research redirect
• the repository's Site checks workflow will perform the full Jekyll build and internal-link check

The experimental social card is intentionally excluded from this pull request.