Remove "Heading 1" in markdown editor

## Is your enhancement request related to a problem? Please describe

The title is already in h1, having multiple h1 in the content is not good for SEO.

## Describe the solution you'd like

![image](https://github.com/user-attachments/assets/9dae3d5b-f39b-4ca7-9857-78604dab3352)


- Remove "Heading 1" in type dropdown
- Change the icon to `type-h2`