feat(decopilot): add built-in render_html tool

[guitavano]

Summary

• Adds a new render_html built-in tool that lets the agent render arbitrary HTML inline in the chat via a sandboxed iframe (allow-scripts only, no allow-same-origin)
• The iframe auto-resizes based on content height via postMessage + ResizeObserver
• Includes an expand button (visible on hover) that opens a near-fullscreen modal with the rendered HTML and an X button to close
• Tool is read-only, no server-side execution — HTML is passed through to the frontend

Test plan

• Start dev server with bun run dev
• Ask the agent to "render an HTML table" or "show me a bar chart" — verify it calls render_html
• Verify the HTML renders in a sandboxed iframe inline in the chat
• Verify the iframe auto-resizes to fit content
• Hover over the iframe and verify the expand button appears
• Click expand and verify the near-fullscreen modal opens with the HTML preview
• Click X to close the modal
• Verify bun run check and bun run fmt pass

🤖 Generated with Claude Code

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Summary by cubic

Adds a built-in render_html tool that lets the agent render HTML inline in chat using a sandboxed iframe. Includes auto-resize and a fullscreen preview; no server-side execution.

• New Features
  • Introduced render_html tool (read-only) that passes HTML to the client; schema via zod, returns { html }.
  • UI renders HTML in an iframe with sandbox="allow-scripts", auto-resizes via postMessage + ResizeObserver, and adds a hover “expand” button to open a near-fullscreen modal.
  • Wired into the tool registry and assistant message renderer.
  • Updated prompting guidance in constants to suggest render_html for charts, tables, and interactive previews.

^{Written for commit 106fb88. Summary will update on new commits. Review in cubic}

[github-actions]

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[github-actions]

Release Options

Suggested: Minor (2.282.0) — based on feat: prefix

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Reaction	Type	Next Version
👍	Prerelease	2.281.4-alpha.2
🎉	Patch	2.281.5
❤️	Minor	2.282.0
🚀	Major	3.0.0

Current version: 2.281.4-alpha.1

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