Add tooltips and accessible labels for all site icons

[Copilot]

Pull Request Template: Add a Conference or Workshop

Thank you for contributing! Most PRs are to add a new conference or workshop. The following are to help ensure you've added everything correctly:

Conference/Workshop Details

• Name, Location, Date(s), Website URL and Status are required (N/A: no conference data change)
• X / Twitter is Optional (N/A: no conference data change)
• Location should be City + Country or Online (N/A: no conference data change)
• Status can include information about registration, pricing, calls for proposals and can include links to all the above. (N/A: no conference data change)

Checklist

• I have added the conference/workshop to the correct YAML file (_data/current.yml or _data/past.yml) (N/A: no YAML updates)
• The entry includes name, location, date(s), url and accurate status (N/A: no YAML updates)
• The entry is in chronological order (soonest to furtherest away) (N/A: no YAML updates)
• If there are any special characters in the name field (: or ; or '), the name must be in quotes (") (N/A: no YAML updates)
• I have checked for duplicates to avoid listing the same event twice (N/A: no YAML updates)
• Build runs successfully (N/A in this PR scope)

Additional context

This change adds tooltip text and accessible labeling for every icon used in templates as the UI shifts toward icon-first affordances. It standardizes icon semantics so standalone icons are announced meaningfully and decorative icons inside labeled links are not double-announced.

• Icon accessibility updates

  • Added title + aria-label (with role="img") for standalone semantic icons (calendar, location, status).
  • Applied to index.html and past.html conference metadata icons.

• Decorative icon handling

  • Set aria-hidden="true" for icons inside already-labeled links (footer social links, 404 home button icon, past page linked X/video icons).
  • Kept tooltip text where icon hover context is useful.

• Files touched

  • index.html
  • past.html
  • 404.html
  • _includes/footer.html

• Representative snippet

  <i class="fa fa-calendar" role="img" aria-label="Dates" title="Dates"></i>
  ...
  <a ... aria-label="GitHub" title="GitHub">
    <i class="fa-brands fa-github fa-2x" aria-hidden="true"></i>
  </a>