fix: keep presence avatars visible across note view modes

[dtkav]

Fixes #108

Summary

• re-resolve and move the existing awareness surface when a Markdown view switches between Live Preview and Reading mode
• anchor to the active mode content when the inline title is unavailable
• give the facepile its own row on narrow viewports and clamp the participant popover to the viewport

Validation

• npm test -- --runInBand --silent — 100 suites, 1,485 tests passed
• npx tsc --noEmit --skipLibCheck
• targeted ESLint and staging build
• exact PR bundle verified on live1 and live2
• visual verification in Live Preview and Reading mode with the inline title hidden, on desktop and app.emulateMobile(true) at 390×844; no note-content overlap and the popover remained within viewport bounds