feat(web): render the font previews with the real surfaces

The interface row loses its preview (the interface itself is the
preview), the prompt row embeds the live composer editor, the code row
renders the diff panel's file diff, and the terminal row mounts the
Ghostty canvas renderer against a local echo loop.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
a7b35a26d8Julius Marminge committed on 8/4/2026, 4:22:55 PMparenta0ac88f
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