Replaces the free-text family inputs with dropdowns of curated faces
filtered through document.fonts.check so only fonts that will actually
render are offered (bundled webfonts always appear); a Custom… option
keeps arbitrary families possible. Each option renders in its own face,
and every row gains a preview card styled like the real surface — chat
text, a mini composer, a highlighted code snippet, and a dark terminal
prompt — rendered in the resolved stack, matching mobile's Appearance
screen style.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>