Improve modal overlay UI: add border and semi-transparent background

Enhance the sync modal overlay visibility and aesthetics:
- Add 1px border to content widget using palette(mid) for theme adaptation
- Restore semi-transparent background (alpha=230) to overlay backdrop
- Remove minimum window size constraint (950x550) for better flexibility

The border ensures the overlay is clearly visible in both light and dark
modes, while the semi-transparent background provides visual separation
without completely obscuring the underlying interface

src/qt/palladiumgui.cpp

@@ -264,10 +264,6 @@ PalladiumGUI::PalladiumGUI(interfaces::Node& node, const PlatformStyle *_platfor
     // Check beim Start ausführen
     checkUpdate();
     // --- ENDE EINFÜGUNG: UPDATE CHECKER ---
-
-    // Set minimum window size to prevent UI breaking
-    // Must be set AFTER all widgets are configured to ensure it's not overridden
-    setMinimumSize(950, 550);
 }
 
 PalladiumGUI::~PalladiumGUI()