Add markdown support for assist messages

[krsilas]

Proposed change

This adds markdown support for messages in assist. LLM often return markdown which is currently shown unformatted in the chat interface.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion: https://community.home-assistant.io/t/feature-request-markdown-support-for-assist/670088
• Link to documentation pull request:

Preview of some of the changes

Includes all of the markdown features supported by "marked" as in other parts of home assistant. Here are a few examples:

Before	After

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[home-assistant]

Hi @krsilas

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

Learn more about our pull request process.

Stale

[krsilas]

There is one outstanding layout issue during streaming that drives me nuts:

Bildschirmaufnahme.2025-07-02.um.20.58.50.mov

For some reason the element height of the ha-markdown element does not always match the text content height.
I thought this is related to the shadow root but I build two simple ha-markdown elements that just render the text. One in lit-html and one with vanilla js and only the lit-html version had this issue.

[MindFreeze]

Looks good but the scrolling bug has to be fixed