Fix several race conditions in the iOS interactive dismiss flow:
- Don't skip keyboard close notifications during pan tracking, which
left Dart unaware the keyboard was dismissed
- Guard resignFirstResponder with generation check so reopened keyboards
aren't killed by stale dismiss completions
- Block pan tracking from starting during an in-flight dismiss animation
- Always reset keyboard view bounds when the keyboard opens, not just
when the dismiss animator is still running
- Handle duration=0 keyboard notifications by snapping immediately
- Gate adaptive learning debug output behind kDebugMode
Rewrite the example as a chat UI demonstrating ListenableBuilder,
scroll freeze during interactive dismiss, and proper bottom inset
handling with max(keyboardHeight, safeBottom).
Modernize example Android project from v1 to v2 embedding with
current AGP/Gradle versions.
