docs: Add llms txt

[coliff]

This pull request introduces a new plugin, starlight-llms-txt, to enhance functionality in the website project. It also includes updates to dependencies, configuration files, and styling to support the integration of the plugin and improve the user interface.

Plugin Integration:

• Added starlight-llms-txt plugin: Updated website/astro.config.mjs to include the new plugin in the plugins array, enabling additional features for the project. ([[1]](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-85cc15dfe103c8efb0d4d619255656cd2f2356feddf360e710ff326a71fdbcdeR4), [[2]](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-85cc15dfe103c8efb0d4d619255656cd2f2356feddf360e710ff326a71fdbcdeR25))
• Dependencies updated: Added starlight-llms-txt to website/package.json and website/package-lock.json to manage the plugin's dependencies. ([[1]](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-fae242fbf77a8a9d52625664bc36ea12316586f8a716b41137d897a2b7e3df76L29-R30), [[2]](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-999051457a1934c824a5f8395589ea5e749a581e9f70a43585c885319cb56e64L14-R15), [[3]](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-999051457a1934c824a5f8395589ea5e749a581e9f70a43585c885319cb56e64R7164-R7190))

Styling Enhancements:

• Improved header styling: Added a blur effect and adjusted opacity for the header.header element to enhance visual aesthetics. ([website/src/custom.cssR135-R143](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-83441a4607546a35116e0e3a6d4d263379c09a17091da5cf781da7a5915d1881R135-R143))
• Anchor link focus style: Modified .sl-markdown-content .sl-anchor-link:focus to reduce opacity on focus for better accessibility. ([website/src/custom.cssR135-R143](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-83441a4607546a35116e0e3a6d4d263379c09a17091da5cf781da7a5915d1881R135-R143))

Configuration Updates:

• Spellchecking configuration: Added "llms" to the .cspell.json file to ensure proper handling of new terminology related to the plugin. ([.cspell.jsonR49](https://github.com/htmlhint/HTMLHint/pull/1678/files#diff-4e0f175c840784de9e935f881821905c75a2a125aa57c51268a7fb4496edfbe6R49))

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (95e6a13) to head (f36a264).
Report is 98 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #1678      +/-   ##
===========================================
+ Coverage   96.99%   100.00%   +3.00%     
===========================================
  Files           2         1       -1     
  Lines        1628         1    -1627     
  Branches      335         0     -335     
===========================================
- Hits         1579         1    -1578     
+ Misses         49         0      -49     

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[gemini-code-assist]

Code Review

This pull request adds the starlight-llms-txt plugin to the website, updates the .cspell.json file, and adds some custom CSS styles. The addition of the plugin enables the generation of llms.txt, which is useful for specifying which large language models can crawl the site. The CSS changes enhance the visual appearance of the header and anchor links.