fix: hide side menu on scroll instead of overflow hacks (#2630)

* fix: hide side menu on scroll instead of overflow hacks

Reverts the overflow/positioning workarounds from #2043 and instead
hides the side menu when the user scrolls, preventing it from
overflowing outside the editor's scroll container.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* comments and check

* fix: hide table handles on scroll

Apply the same scroll-hide pattern to table handles.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>