feat: Add Mermaid diagrams to the / menu

[gravelfreeman]

It would be useful to add Mermaid diagrams through the / command menu.

For example, typing /mermaid could insert a Mermaid block into the note:

flowchart TD
    A[Start] --> B[Step 1]
    B --> C[Step 2]

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Suggested behavior

• Add Mermaid to the / menu.
• Insert a Mermaid code block automatically when selected.
• Render the diagram directly in the note.
• Allow users to switch back to/edit the Mermaid source easily.
• Support standard Mermaid diagram types such as flowcharts, sequence diagrams, timelines, mindmaps, etc.

This would be especially useful for study notes, workflows, processes, piecharts, and visual summaries without needing to remember the mermaid commands.

[gravelfreeman]

Crazy you implemented it in the latest beta! I really like it.

I noticed that the colors aren't following the theme's color tokens.

[timothepoznanski]

Fixed in next release.

[gravelfreeman]

I wouldn't put both of these under a Diagrams submenu. Instead, each one should have its own menu entry.

Same for code blocks. I would add a separator under Block Languages and list all the languages directly underneath instead of using a second submenu:

This one also has a second submenu for only a single option, which feels unnecessary:

Calendar and time is the only second-level submenu I would keep:

[timothepoznanski]

Wouldn't that be too many items at the root/or first submenu level? For example for things like programming languages that takes lot of space.

[gravelfreeman]

That's true, but the second-level submenu isn't ideal either.

I would suggest making the section below the separator scrollable, with a maximum of ~10 items visible at a time. That would keep the menu compact while still allowing all options to remain directly accessible in a single sub-menu.