Add links to portfolio and website for each lab member

[gmermoud]

Summary

Adds per-member external link badges (Website and Portfolio) to each collaborator card on the team section of the site.

Changes

• build.py: Added portfolio field to the Collaborator dataclass and _KNOWN_FIELDS. The parser now strips surrounding <> angle brackets from field values (so Markdown auto-link syntax like <https://...> works cleanly in .md files). Rendering logic collects website and portfolio into styled <a> tags separated by · and appends them below the bio.
• index.html: Added .collab-link and .collab-links CSS classes for the link badges. Regenerated HTML reflects links for all members who have a website or portfolio field set.
• data/team/01-gregory-mermoud.md: Added portfolio (Google Scholar) and updated field syntax to use <url> angle-bracket form.
• CLAUDE.md: Added project-level instructions for the build system.
• .gitignore: Added .DS_Store.

Test plan

• Run python build.py and verify index.html is regenerated without errors.
• Open index.html in a browser and confirm link badges appear under bios for members with website/portfolio fields.
• Verify links open in a new tab and that members without links show no badge.
• Check that angle-bracket URLs in .md files are parsed correctly (no < or > in rendered href).