Fix/header projects dropdown fix 2026 02 06

[chengjiahao1234]

Type of Change

Please select the type of change (uncomment one):

✅ Bug Fix
✅ Enhancement / New Feature
✅ Documentation
✅ Styling / CSS

Summary

Briefly describe what this PR changes:

Fixes the header Projects dropdown UX across screen sizes (no caret arrow, dropdown can fully overlap the page instead of being clipped, and mobile navbar collapses back without leaving a large blank header area). Also adds a generated sitemap.xml and updates robots.txt to reference it, plus improves Windows local dev performance by adding wdm.

Changes Made

List specific files or sections changed:

• header.html: Updated Projects dropdown toggle (no caret) and styled AtlasPatch dropdown entry (font/color consistency)
• main.scss: Ensured dropdown menus aren’t clipped (overflow + z-index), improved Projects toggle/button styling, and adjusted AtlasPatch link color
• theme-toggle.js: Fixed --atlas-nav-height behavior so the navbar shrinks correctly after collapsing on small screens
• sitemap.xml: Added generated sitemap at sitemap.xml
• robots.txt: Converted to Jekyll-rendered file and updated Sitemap: to use sitemap.xml
• DEVELOPMENT.md: Updated robots/sitemap URL guidance to match the new templated robots.txt
• Gemfile (+ Gemfile.lock): Added wdm on Windows to avoid Jekyll polling warnings

Testing Checklist

Please confirm you've tested the following:

• Changes display correctly on desktop (1920x1080 or similar)
• Changes display correctly on tablet (768x1024 or similar)
• Changes display correctly on mobile (375x667 or similar)
• Tested in light theme
• Tested in dark theme
• No broken links or images
• No console errors
• Ran bundle exec jekyll serve locally without errors

Screenshots (if applicable)

Related Issues

Additional Notes

1. robots.txt and sitemap.xml are now generated via Jekyll so the sitemap URL stays correct if site.url / baseurl changes.
2. Windows-only wdm dependency prevents file-watcher polling and speeds up local jekyll serve.

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By submitting this PR, I confirm:

• I have tested these changes locally
• I have followed the code standards in DEVELOPMENT.md
• I have updated documentation if needed
• I am ready for this to be reviewed and merged