Fix image center flash during window resize on zoom

[justnullname]

Fixed a visual bug where the image center flickers rapidly every few mouse scrolls when zooming in/out of an image while the "window adapts to image scale" mode is enabled.

The problem was caused by a synchronization issue between the Win32 Desktop Window Manager (DWM) and DirectComposition. When the window is resized and DirectComposition content changes simultaneously, race conditions can cause DWM to render a frame where the window size has updated but the DirectComposition visual tree hasn't been committed yet (or vice-versa), resulting in a one-frame flicker or "jump".

This commit fixes the issue by calling DwmFlush() immediately after g_compEngine->Commit() in OnResize and WM_SIZE. DwmFlush() blocks the calling thread until the next DWM frame is presented, ensuring the DirectComposition changes and window resize are synchronized and rendered in the same frame.

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PR created automatically by Jules for task 6698394441088915593 started by @justnullname

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