4181 swiping down any amount closes image preview even when zoomed in - #4184

Summary

Fixes an issue where swiping down would dismiss the image viewer even when the image was zoomed in.

Changes

• Added zoom state tracking to the image viewer.
• Prevented the swipe-to-dismiss gesture from starting while the current image is zoomed.
• Propagated zoom state changes from NCImageZoomView to the media viewer presenter.
• Introduced a dedicated callback (onZoomChanged) to synchronize zoom state across the viewer hierarchy.

Additional Improvements

• Refactored NCMediaViewerPageModel into an observable object to allow page state updates without recreating the SwiftUI view hierarchy.
• Updated page rendering to observe state changes directly instead of rebuilding the hosting view.
• Preserved SwiftUI view state (including image loading and zoom state) during page updates.
• Eliminated the visible white flash that could occur while transitioning from placeholder/loading states to the final image, especially with large images and Live Photos.

Result

• Swiping down no longer dismisses the viewer while the image is zoomed.
• Image dismissal behaves correctly once the zoom returns to its default scale.
• Page updates are smoother and no longer recreate the entire view hierarchy.
• Improved visual stability during image and Live Photo loading.