fix: don't render content as title in callouts with empty titled paragraph

[r4ai]

fix #116

Fixed an issue where the body was displayed as the title in callouts with a title consisting only of line breaks.

Example:

> [!IMPORTANT]  
> Crucial information necessary for users to succeed.

yields:

<div data-callout data-callout-type="important">
  <div data-callout-title>Important<br>
  </div>
  <div data-callout-body>
    <p>Crucial information necessary for users to succeed.</p>
  </div>
</div>

[changeset-bot]

🦋 Changeset detected

Latest commit: 2effedc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@r4ai/remark-callout	Minor

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