Add automated broken link checking for documentation

[ShivamJha2436]

Summary

This PR adds an automated broken-link checker for Contour documentation using the Lychee GitHub Action.

Behavior

• Runs on pull requests that modify files under site/content/docs/main
• Runs weekly on a scheduled basis to detect documentation link rot
• Generates a Markdown report of broken links
• Automatically opens a GitHub issue on scheduled failures
• Prevents duplicate issue spam by checking for an existing open issue first

Why

Broken links in documentation negatively impact users and contributors.
This workflow provides early detection while keeping CI cost low by scanning only the actively maintained main docs.

Files Added

• .github/workflows/docs-link-check.yml
• .lycheeignore

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.77%. Comparing base (d368385) to head (0ee4bfe).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7399      +/-   ##
==========================================
- Coverage   81.85%   81.77%   -0.09%     
==========================================
  Files         130      130              
  Lines       15766    15766              
==========================================
- Hits        12906    12893      -13     
  Misses       2576     2576              
- Partials      284      297      +13     

see 1 file with indirect coverage changes

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