FB IAB on Xiaomi (and similar WebViews that don't shrink 100dvh) keeps
the chat input covered by the soft keyboard. Fix by writing the
visualViewport-derived keyboard height to a CSS variable on <html> and
consuming it as padding-bottom on the chat input bar.
- Add useKeyboardHeight hook (visualViewport + rAF batching, no re-renders)
- Apply --keyboard-height + env(safe-area-inset-bottom) to .bar padding
- Add scrollIntoView on textarea focus so the input stays visible
- Add viewportFit: cover so safe-area-inset-bottom is reported
admin
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