Frontmatter support

**Is your feature request related to a problem? Please describe.**
It is getting more and more common to have ai yaml based frontmatter in markdown files. As it stands right now, this renders oddly and look awkward in the editor.

**Describe the solution you'd like**
An option to either ignore or render as a table the front matter when rendered to html. The editor should keep it plain text with no formatting if it detects that it is a yaml based frontmatter.

**Describe alternatives you've considered**
giving up on the editor completely. My backend processor already strips the frontmatter when it does its conversion from markdown to html, but I would like to keep it in the editor for a better user experience.

**Additional context**
[specification](https://www.markdownlang.com/advanced/frontmatter.html)
```markdown
---
subject: my-awesome-example
frontmatter: matters
summary: this is just an example of what frontmatter looks like, it would exist on the top of the document and contains yaml. AI agents can use this to quickly identify if the document should be read or not based on the contextual clues in the frontmatter. This summary is one line, it just word wraps in the editor.
last-updated: June 10, 2026
---

# Body of document starts here
```

Reproduce the supplied YAML frontmatter example in the editor and inspect how it is currently rendered to HTML. Define acceptance around detecting the delimited block, keeping it unformatted in the editor, and choosing whether HTML ignores it or renders it as a table.

Written by the indexing model from the issue text.