Introduce smooth UI transitions by adding opacity-based animations. Import QGraphicsOpacityEffect and add animate_widget_fade_in, animate_widget_fade_out, and set_status_message_animated to cross-fade status text and fade buttons in/out. Update signal handlers and download flow to use the new animated status setter and fade methods instead of direct setText/setVisible calls. Keep animation references on widgets to avoid premature GC and remove effects after fade-out.
oop7
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