fix: preserve PNG transparency in chat wallpapers

Remove .forceOpaque = true from ChooseFromFile in settings_chat.cpp, which was compositing transparent pixels against white via Opaque() for all non-JPEG files before the image reached the wallpaper pipeline.

Author: pratikpatel8982

Telegram/SourceFiles/settings/sections/settings_chat.cpp

@@ -707,7 +707,7 @@ void ChooseFromFile(
 		auto image = Images::Read({
 			.path = result.paths.isEmpty() ? QString() : result.paths.front(),
 			.content = result.remoteContent,
-			.forceOpaque = true,
+			.forceOpaque = false,
 		}).image;
 		if (image.isNull() || image.width() <= 0 || image.height() <= 0) {
 			return;