[BUG] Diff/code block icons render as tofu (☒) in VS Code Extension chat panel due to CSP blocking base64 font

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

In the VS Code Extension chat panel, diff view icons (line numbers, +/- indicators)
render as broken characters (☒/tofu) instead of the intended glyphs.

What Should Happen?

Diff/code block icons render correctly in the chat panel.

Error Messages/Logs

Icons appear as ☒ (tofu) squares. Affected elements include:
- Line number indicators in code blocks
- `+` / `-` diff markers in file edit previews

Steps to Reproduce

1. Open VS Code with the Claude Code extension
2. Ask Claude to edit a file (triggers diff view in chat panel)
3. Open Developer: Open Webview Developer Tools → Console tab
4. Observe CSP font-src violation error
5. Observe ☒ rendering in the chat panel

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

VS Code 1.109.4

Claude Code Version

2.1.39

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Host the icon font on https://*.vscode-cdn.net or include it as a bundled asset
accessible via vscode-resource: scheme, so it complies with the Webview CSP policy.