Redesign Projects page as a professional case-study portfolio

[sabujcb]

Summary

• replace the basic category listing with a polished, responsive Projects landing page
• add a strong portfolio introduction, summary metrics, and category navigation
• present all six projects as metric-led case-study cards with status, outcomes, methods, and tools
• preserve the earlier project findings and validation context
• link the three verified Joint-RPCA repositories and authoritative method documentation for projects without public code
• support dark mode, mobile layouts, keyboard navigation, and reduced-motion preferences

Resource policy

• public code links are shown only when a matching repository was verified
• other external links point to official Gemelli, mia, scikit-learn, XGBoost, SciPy, or Torchvision documentation
• no repository or implementation link was invented for private/unpublished project code

Validation

• npm run lint:prettier
• YAML/front-matter parsing for all project files
• unique project order and complete metadata checks
• HTTPS resource validation and Liquid block-balance checks
• git diff --check
• Jekyll build delegated to the PR's GitHub Actions check