Add Astro Starlight links validator extension and fix broken documentation links - #758

This PR addresses broken links in the documentation by implementing automated link validation using the starlight-links-validator plugin for Astro Starlight.

Problem

The documentation had several issues:

• Missing alias-triggers.md file referenced throughout the docs
• No automated link validation during build process
• Potential for broken links to be introduced without detection

Solution

1. Added Starlight Links Validator Plugin

• Installed starlight-links-validator@0.17.2 as a dependency
• Configured the plugin in astro.config.mjs with appropriate settings:

  starlightLinksValidator({
    errorOnRelativeLinks: false,
    errorOnLocalLinks: false,
  })

• This configuration allows Starlight's standard relative link format while catching genuinely broken links

2. Created Missing Documentation

Added comprehensive docs/src/content/docs/reference/alias-triggers.md covering:

• @mention-style command triggers (/command-name syntax)
• Context text access via ${{ needs.task.outputs.text }}
• Visual feedback options with emoji reactions
• Security considerations and permission model
• Common use cases and examples
• Integration with other trigger types

3. Enhanced Build Process

• Added validate-links npm script for standalone link validation
• Link validation now runs automatically during documentation builds
• Build process fails with clear error messages when broken links are detected

Validation

The implementation successfully validates all documentation links:

• ✅ All 17 documentation pages pass validation
• ✅ Plugin correctly identifies broken absolute links while allowing valid relative links
• ✅ No security vulnerabilities introduced (CodeQL clean)
• ✅ All existing tests pass

Testing

The validator was tested to ensure it:

1. Allows valid relative links (e.g., [text](file.md))
2. Catches broken absolute links (e.g., [text](/missing/path/))
3. Integrates properly with the Astro build pipeline
4. Provides clear error reporting when issues are found

This ensures robust documentation link integrity going forward while maintaining the existing Starlight link conventions.

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