docs: Update site audit to mark completed cleanup tasks

Marked the following as completed (Jan 31, 2026):
- Removed Google+ widget from index.html
- Removed html5shim references from 16 HTML files
- Fixed news.html section ID typo (June2024 → June2025)
- Updated HTTP URLs to HTTPS across site
- Removed WormClassroom compromised link from science.html

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: slarson