Update GitHub Pinned Repos to Balance AI/ML and Physics

GitHub pinned repos are currently all physics-focused. Target roles are AI/ML-heavy. Pin selection should reflect both domains to match positioning as an AI Research Engineer with computational science depth.

Acceptance Criteria

• [ ] Review current 6 pinned repos
• [ ] Select 2-3 AI/ML repos to pin (LLM work, ML systems, or applied AI projects)
• [ ] Keep 2-3 physics/computational repos that show scientific depth
• [ ] Ensure pinned repos have clean READMEs with clear descriptions
• [ ] Update DISCOVERY.md action item status to DONE