Fix site reliability and add validation

[jviers]

What changed

• Added safe portrait and project-image fallbacks, lazy loading, and useful alternative text.
• Corrected two case-sensitive image filenames that failed on GitHub Pages.
• Fixed People-page related-content loading so direct profile links do not race undefined data.
• Changed project and publication filters to exact class matching.
• Corrected malformed project markup, location labels, and inaccurate hard-coded date metadata.
• Added user-visible CSV load failure messages.
• Added a Python CSV/asset validator and GitHub Actions workflow.
• Added a maintainer checklist for approved collaborator photos, stale content, dependency upgrades, and image optimization.

Why

The audit found broken images on GitHub Pages, a People modal race condition, false-positive filters, silent content-loading failures, malformed HTML, and no automated enforcement of the CSV-to-asset contracts.

Impact

The public site now degrades gracefully when portraits are missing, uses exact filters, loads direct person links reliably, and rejects future CSV/image mismatches in pull requests. Missing approved portraits remain documented human follow-up items rather than broken images.

Validation

• Parsed all 6 changed inline scripts without syntax errors.
• Validated 212 CSV records with 0 errors.
• Imported all 5 CSV files through the bundled spreadsheet runtime and rendered the collaborators table.
• Ran Python syntax compilation and git diff --cached --check successfully.
• Confirmed images/agave.png is unrelated, untracked, and excluded from the commit.