Just make outline of markdown to be structured:

<img width="282" height="144" alt="image"
src="https://github.com/user-attachments/assets/6c7e5d5f-ae09-47a9-965a-6f9f9b731ce6"
/>

Release Notes:

- Added structured outline for Markdown.
- Also fixed the breadcrumb display in Issue
[#45663](https://github.com/zed-industries/zed/issues/45663).