Removes the temporary on-screen scroll diagnosis panel and the global
window.__scrollAtClick stash. The anchor scrollTop is now captured
synchronously at addStackedNote entry and threaded through
scrollToFocusedNote and scrollToNoteElement to scrollToElement, so no
state survives across calls — nothing to reset on repo or page change.
Capture mainApp.scrollTop synchronously when addStackedNote runs and
snap the scroll back to that value before scrollIntoView fires, so
the smooth scroll begins from where the user actually tapped rather
than from a position drifted by momentum or async work.
Native scrollIntoView reads the element position at scroll time and
picks the right scrollable ancestor itself, sidestepping iOS Safari
quirks with scrollTo on overflow containers and visual-viewport shifts.
Replace the (index + 1) * clientHeight math and 80ms setTimeout with a
scrollToElement helper that reads getBoundingClientRect inside rAF, so
the smooth scroll starts from the user's actual position even when the
note is freshly mounted.
body/html have overflow:hidden so scrollTop is a no-op on them.
#main-app is the actual scroll container; use overflow-y:auto on
mobile and target it directly in scrollToNote and the scroll listener.
