- Dart-side animation replay using exact native curve (21-point lookup
table sampled from CADisplayLink) with 16ms start offset and 10ms
shorter duration to stay ahead of the native animation pipeline.
- Snap-back reads bounds presentation layer so height doesn't jump.
- Dismiss defers resignFirstResponder until bounds animation completes,
with immediate Dart close animation via animTarget/animGeneration.
- enableInteractiveDismiss accepts trackingInset to widen the gesture
zone above the keyboard (for composer height).
- FFI: anim_target, anim_duration, anim_gen, system_keyboard_height,
is_tracking exposed for Dart animation and scroll physics.
