Contain horizontal overflow within #main-app instead of leaking to the
document, which caused a horizontal scrollbar to consume viewport height
and trigger an unwanted vertical scrollbar. Also fix note pane height
to use 100% instead of 100vh, and switch useResizeContainer to minWidth
so the flex container can grow when the window is wider than the notes.
Add a window resize listener to keep the value accurate on resize.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
