fix(onboarding): Clip the SCM reveal during its exit tween

[jaydgoss]

TLDR

ScmCollapsibleReveal did not clip its content while collapsing, so the exit tween spilled over whatever sat below it. Overflow now rides the animation targets instead of React state, which is the only way to reach an exiting child.

Details

AnimatePresence renders an exiting child from renderedChildren, React state holding the element captured when it was last present. This component drove overflow through useState into style={{overflow}}, and onAnimationStart fired setOverflow('hidden') on collapse. That re-render produces a new element which is then discarded, because AnimatePresence keeps rendering the frozen one carrying overflow: visible. The whole collapse ran unclipped.

The existing openRef was a workaround for the same trap one level over, in the completion callback's closure. It does not help here: nothing routed through React props reaches an exiting child.

Overflow now comes from the animation targets, which bypass reconciliation and write through the value pipeline:

• initial and exit set overflow: hidden
• animate releases it with transitionEnd: {overflow: 'visible'}

Two framer-motion behaviors this leans on, both verified in 12.38.0 rather than assumed:

• isAnimatable('hidden') is false, so canAnimate fails and AsyncMotionValueAnimation applies the value immediately, before makeAnimationInstant. The clip lands at the start of the collapse instead of being tweened across it.
• With initial={false}, makeLatestValues uses the animate target and folds transitionEnd keys into the starting values, so a settled-open mount begins at overflow: visible. That matches the previous useState(open ? 'visible' : 'hidden').

Open behavior is unchanged. The state, the ref, and both animation callbacks are no longer needed.

This was latent rather than new: every consumer (ScmCollapsibleSection, ScmAlertOptionCard, ScmAlertFrequencySection, ScmIssueAlertNotificationOptions) had the same unclipped collapse. Their content is short and none of them sit inside a bordered card, which is probably why it went unnoticed.

Refs VDY-150

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[linear-code]

VDY-150