WIP: implement opt-in frontmatter tools (refs #1055)

[Meh10t]

Refs #1055

This is a draft PR to track incremental work on frontmatter support.

Initial commit sets up the branch and TODO markers.

Next steps:

• Implement MemoryAddFrontmatterTool
• Implement MemoryGetFrontmatterTool
• Integrate frontmatter display when tool is enabled
• Add tests

[Meh10t]

Hi @MischaPanch,

I just opened this draft PR to track my work on issue #1055 (frontmatter opt-in tools).
I will continue implementing the feature incrementally and push updates soon.
Let me know if you have any guidance or preferred approach before I proceed further.

Thanks!

[MischaPanch]

I think we specified the requirements fairly completely, so unless you have more questions, I don't have much to add. Note that tools are made opt-in by inheriting from the corresponding marker class.

The best way to test this feature is likely through temporary files