feat: screenshot app improvement, WIndow Server supports full-screen overlay, Disks app UI improvements

programs/include/gui/window.hpp

@@ -67,6 +67,7 @@ struct Window {
     bool external;      // true = shared-memory window from external process
     int  ext_win_id;    // window server ID (valid when external == true)
     uint8_t ext_cursor; // cursor style requested by external app (0=arrow, 1=resize_h, 2=resize_v)
+    uint32_t ext_flags;
 
     Rect titlebar_rect() const {
         return {frame.x, frame.y, frame.w, TITLEBAR_HEIGHT};