feat(FR-433): wrap customTags contents with Collapse

[agatha197]

resolves #3066 (FR-433 / parent: FR-432)

Adds support for GitHub Flavored Markdown (GFM) and custom tag parsing in chat messages. This enhances markdown rendering with features like tables, task lists, and collapsible sections for tagged content (e.g., "think" tags).

Key changes:

• Added GFM support through remark-gfm plugin
• Implemented custom tag parsing to extract and display tagged content in collapsible panels
• Enhanced code block styling and layout
• Added KaTeX for math equation rendering

Checklist:

• Documentation
• Test case(s) to demonstrate the difference of before/after

[agatha197]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• feat(FR-433): wrap customTags contents with Collapse #3073 👈 (View in Graphite)
• feat(FR-434): support math in model card. #3067
• main

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