chore: test app memory leaks

[abelonogov-ld]

Note

Low Risk
Low risk: changes are confined to test-app UIKit presentation/cleanup code and mainly adjust view controller containment and closure captures to avoid retain cycles/leaks.

Overview
Fixes potential memory leaks in DialogsUIKitViewController by updating the dismissal cleanup closures to capture timerVC/dimView weakly.

Also makes the Current Window Sizing overlay use proper view-controller containment (addChild/didMove and corresponding willMove/removeFromParent) so the embedded CountdownTimerViewController is correctly detached on dismissal.

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