Brave Android (custom bottom toolbar) and some other mobile browsers report
dvh taller than the actually visible area while position:fixed elements track
the visible viewport — so 100dvh containers extended under the browser tab
bar and the bottom of every page could never be scrolled into view.
main.ts now keeps --visual-viewport-height synced to window.innerHeight
(resize / orientationchange / visualViewport events — the same reference
frame as the fixed tab bar), and the dashboard shell, chat, and app-session
mobile heights consume it with 100dvh as fallback. The app now scales with
the browser chrome as it shows/hides. Scroll clearance margin 16px → 28px.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
