Re-add preventDefault on mousedown so the textarea doesn't blur when
the user taps send — keyboard stays up, no viewport reflow jumping
the input to the top of the screen. The action still runs on click
(which fires reliably from the iOS touch sequence even for quick
taps), so this preserves the previous fix's quick-tap reliability.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
da36f8feb4