Fix typo in accessibility chat mode filename

[Copilot]

Summary

This PR corrects a spelling error in the accessibility chat mode filename. The file was incorrectly named accesibility.chatmode.md (with only one 's') when it should be accessibility.chatmode.md (with two 's's).

Problem

As reported in the issue, the misspelled filename was causing confusion and undermining the credibility of the repository, particularly problematic for a file that provides guidance on Web Content Accessibility Guidelines (WCAG) 2.1. The typo was visible in:

1. The VS Code file explorer (see screenshot showing accesibility.chatmode.md)
2. The VS Code chat mode selector dropdown
3. All documentation referencing the file

Changes

• Renamed file: chatmodes/accesibility.chatmode.md → chatmodes/accessibility.chatmode.md
• Updated references: All references in README.chatmodes.md now point to the correctly spelled filename, including:
  • File path links
  • VS Code installation URLs
  • VS Code Insiders installation URLs

Verification

• ✅ Confirmed no other files in the repository reference the old misspelled filename
• ✅ Ran the build script (node update-readme.js) to ensure all generated files are up-to-date
• ✅ Verified the file content remains unchanged (only the filename was corrected)

This is a minimal, surgical fix that addresses the reported issue without modifying any functionality or content.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Typo in 'Accesibility.md' file.</issue_title>
<issue_description>Hello,

I was sent this repo by a colleague and was initially skeptical that this was a legitimate tool due to 'accessibility' being spelled wrongly. This shows up incorrectly as well in VS code. Please fix!

</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #339

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[Copilot]

Pull Request Overview

This PR corrects a spelling error in the accessibility chat mode filename from accesibility.chatmode.md (one 's') to accessibility.chatmode.md (two 's's). The typo was visible in VS Code's file explorer and chat mode selector, undermining the repository's credibility, particularly for a file providing WCAG 2.1 guidance.

Key changes:

• Renamed the chat mode file from accesibility.chatmode.md to accessibility.chatmode.md
• Updated all references to the file in README.chatmodes.md including file paths and installation URLs