feat(tool): markitdown fetch adapter

[EvgeniyPeshkov]

MarkItDown adapter that converts web pages and files to markdown using the
markitdown CLI tool. It provides:

• fetch_webpage tool — allows LLM agent to fetch and convert web pages to markdown during a chat session
• /fetch slash command — letting users manually fetch web pages into chat's context

Advantages

• various formats are supported: html, pdf, docx, etc
• tools can fetch from local files
• improved privacy as conversion is done locally
• no API access to third-party services

Supporting Documentation

https://github.com/microsoft/markitdown

AI Usage

CodeCompanion assisted with prototyping this new feature for CodeCompanion (=.
However, the final implementation was largely rewritten by hand.

Related Issue(s)

N/A - new feature.

Screenshots

N/A — no UI changes.

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I confirm that this PR has been majority created by me, and not AI (unless stated in the "AI Usage" section above)
• I've run make all to ensure docs are generated, tests pass and StyLua has formatted the code
• (optional) I've added test coverage for this fix/feature
• (optional) I've updated the README and/or relevant docs pages

[olimorris]

This looks fantastic! Thank you for sharing.

I'm planning on moving away from Plenary at some point this year. Can you switch the Plenary.Job module out for vim.system?

Also, I propose we make this the default adapter for fetching web pages.

[EvgeniyPeshkov]

Glad you like it!
No problem—I’ve switched to vim.system() in 3e4609a.
Would you like to make this the default adapter in this PR or tackle it later? If you confirm, I can handle it right here.