Draft: Enable markdownlint link-fragments check for translated docs

What does this MR do?

1. Adds a new CI job docs-i18n-lint links that validates anchor links in internationalized documentation by:
   • Creating fallback symlinks for missing locale files to the original English docs
   • Running lychee with offline mode and fragment checking on all locale directories
   • Enabling the link-fragments rule in markdownlint configuration
2. Enables markdownlint's MD051 (link-fragments) rule for /docs-locale to validate that internal anchor links point to existing headings.
   • https://github.com/DavidAnson/markdownlint/blob/main/doc/md051.md

This ensures that internal anchor links work correctly across all documentation locales.

To QA and Test

1. Check what locale directories exist ls -la doc-locale
2. See what symlinks get created ./scripts/docs_i18n_verify_links.sh
3. Verify symlinks were created correctly find doc-locale/ -type l | head -10
4. Test lychee directly on a specific locale lychee --offline --include-fragments doc-locale/ja-jp

Test the markdownlint changes

cd doc-locale && markdownlint-cli2 --config .markdownlint/.markdownlint-cli2.yaml '**/*.mdThis MR turns on markdownlint's link-fragment for /doc-locale

Why are we doing this?

Previously, translated documentation could contain broken anchor links that went undetected. With the recent addition of English anchor links to all translated headings (e.g., ## はじめに {#introduction}), we can now properly validate these links.

This helps ensure:

• All internal anchor links in translated docs are valid
• Users can navigate seamlessly between language versions
• Broken links are caught during CI/CD

Related issues

Related https://gitlab.com/gitlab-com/localization/docs-site-localization/-/issues/333#note_2829368424

Checklist

See Definition of done.

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Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green.
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
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• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.