Revert "Fix hiding the main UI window while streaming on Qt 6.7"

The original issue on Qt 6.7 was caused by conflicts with the window state set in main.qml
which was addressed by afbc49e39a.

The remaining issue with Qt 6.7 clobbering window state and position when hiding a window
looks like a legitimate Qt bug.

This reverts commit ebe270bec5.

app/gui/StreamSegue.qml

@@ -38,7 +38,7 @@ Item {
         hintText.visible = false
 
         // Hide the window now that streaming has begun
-        window.hide()
+        window.visible = false
     }
 
     function displayLaunchError(text)
@@ -67,7 +67,7 @@ Item {
         stackView.replace(stackView.currentItem, component.createObject(stackView, {"appName": appName}), StackView.Immediate)
 
         // Show the Qt window again to show quit segue
-        window.show()
+        window.visible = true
     }
 
     function sessionFinished(portTestResult)
@@ -94,7 +94,7 @@ Item {
             stackView.pop()
 
             // Show the Qt window again after streaming
-            window.show()
+            window.visible = true
 
             // Display any launch errors. We do this after
             // the Qt UI is visible again to prevent losing