chore(ci): fix broken links in markdown files

[rnbguy]

Closes: #1142

Description

• fixes dead markdown links
• enable dead link checks for docs directory on pull requests
• enable dead link checks for all *.md files on main

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PR author checklist:

• [ ] Added changelog entry, using unclog.
• [ ] Added tests.
• [ ] Linked to GitHub issue.
• [ ] Updated code comments and documentation (e.g., docs/).
• [ ] Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• [ ] Reviewed Files changed in the GitHub PR explorer.
• [ ] Manually tested (in case integration/unit/mock tests are absent).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 64.06%. Comparing base (5407030) to head (052e7a9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1143 +/- ## ======================================= Coverage 64.06% 64.06% ======================================= Files 217 217 Lines 21049 21049 ======================================= Hits 13484 13484 Misses 7565 7565 ```

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