docs: Change absolute URLs to relative paths in error messages guide

Convert shakacode.com absolute URLs to relative markdown paths:
- Auto-Bundling Guide -> ../core-concepts/auto-bundling-file-system-based-automated-bundle-generation.md
- Server Rendering -> ../core-concepts/react-server-rendering.md
- Component Registration -> ../api-reference/javascript-api.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

docs/guides/improved-error-messages.md

@@ -197,6 +197,6 @@ If you encounter issues:
 
 ## Related Documentation
 
-- [Auto-Bundling Guide](https://www.shakacode.com/react-on-rails/docs/guides/file-system-based-automated-bundle-generation/)
-- [Server Rendering](https://www.shakacode.com/react-on-rails/docs/guides/server-rendering/)
-- [Component Registration](https://www.shakacode.com/react-on-rails/docs/guides/component-registration/)
+- [Auto-Bundling Guide](../core-concepts/auto-bundling-file-system-based-automated-bundle-generation.md)
+- [Server Rendering](../core-concepts/react-server-rendering.md)
+- [JavaScript API (Component Registration)](../api-reference/javascript-api.md)