feat: HTML file cards should render inline in chat like the Markdown preview

Hello,

HTML files displayed in chat only appear as a "click to open" card, while Markdown files render directly inline, so viewing a generated report requires an extra tap and a full-screen context switch.

Current behavior

• .md file cards render their content directly in the chat message.
• .html file cards only open a separate full-screen preview view (iframe + toolbar) when tapped.

Desired behavior

• Render the HTML document inline in the chat card: height-capped (e.g. 300–400 px), internally scrollable, and rendered in a sandboxed iframe pointing at the existing /api/workspace/files/serve/<path> endpoint.
• The existing full-screen preview view stays available as a secondary action (e.g. an "expand" affordance on the inline card).
• Include a cache-busting parameter in the inline iframe URL so the preview always reflects the current file.

Acceptance criteria:

• .html file cards render the document inline (height-capped, scrollable) without an extra tap.
• Tapping the inline card (or an explicit expand button) opens the existing full-screen preview.
• The inline iframe uses a cache-busting URL parameter.
• Behavior is verified for a self-contained HTML file.

Thanks for considering this. It would make HTML artifacts (reports, dashboards, generated documents) as glanceable as Markdown, especially on mobile.

Best regards,
Joshua Krimmer

Start by locating the chat file-card renderer for Markdown and the existing HTML full-screen preview that uses the /api/workspace/files/serve/<path> endpoint. Add the inline HTML card with a capped, scrollable sandboxed iframe and a cache-busting URL, while preserving expansion to the full-screen view; verify it with a self-contained HTML file.