add: callout title prop

[x0rgus]

Summary

Adds support for an optional title prop to the Callout component.

This allows callouts to display a heading above their content, improving readability and structure in documentation.

Changes

• Added title?: ReactNode to CalloutProps
• Render title above callout content
• Added callout-title component part for styling
• Added Storybook example demonstrating the feature
• Added Storybook control for the title prop

Test Plan

• Ran Storybook locally (pnpm storybook)
• Verified title renders correctly across variants
• Ran pnpm lint
• Ran pnpm build

Related

Resolves: https://github.com/orgs/mintlify/discussions/2965

---

Note

Low Risk
Low risk UI-only change: adds an optional title render block and Storybook controls/examples, with minimal impact to existing callout behavior.

Overview
Adds an optional title prop to Callout that renders a bold heading above the callout body and exposes it via a data-component-part="callout-title" hook.

Updates Storybook to document/control the new prop and adds a WithTitle story demonstrating the feature.

^{Written by Cursor Bugbot for commit 3745399. This will update automatically on new commits. Configure here.}