Fix(preventScreenshot): fix logic on iOS

[marineshaw]

Bug fixed : Opening Control Center during app launch causes the screenshot prevention overlay to get stuck visible on iOS. The overlay remains on screen while the app is fully active, producing a white screen over the app content. Subsequent background/foreground transitions are also affected.

File: RNASAppLifecyleDelegate.swift

Change: Added private var becomeActiveObserver: NSObjectProtocol?
Why: Holds a reference to the NotificationCenter observer for proper cleanup in deinit
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Change: Added _ = launchScreen.view in the lazy launchScreenWindow initializer
Why: Forces the storyboard view controller to load its view eagerly, so the overlay renders its content immediately instead of showing a blank white window on first display
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Change: In didFinishLaunchingWithOptions: subscribe to UIApplication.didBecomeActiveNotification via NotificationCenter
Why: This notification is posted directly by UIKit at the OS level, independently of Expo's delegate chain. It fires reliably when the app becomes active even during launch, where the delegate method is dropped
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Change: Added deinit to remove the NotificationCenter observer
Why: Prevents a memory leak if the delegate is ever deallocated
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Change: Replaced launchScreenWindow?.makeKeyAndVisible() with launchScreenWindow?.isHidden = false in applicationWillResignActive
Why: makeKeyAndVisible() steals key window status from the main app window, which triggers cascading willResignActive events from internal app activity, causing the overlay to re-appear unexpectedly. The window's .alert + 2 level already guarantees it appears on top without needing key window status
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Change: Added a comment to applicationDidBecomeActive
Why: Kept as belt-and-suspenders fallback in case the NotificationCenter observer is not set up (e.g. preventRecentScreenshots is toggled at runtime)