ios: show spinner for database operations moved to sub-screen (#7228)

The settings reorganization (#7005) moved Export, Import and Start chat
into the pushed "Database passphrase & export" sub-screen, but the
progress spinner stayed as an overlay on the parent screen, hidden
behind it. Add the same overlay to the sub-screen so the spinner is
visible during these operations, matching DatabaseEncryptionView.

apps/ios/Shared/Views/Database/DatabaseView.swift

@@ -252,6 +252,11 @@ struct DatabaseView: View {
             runChatToggleView()
         }
         .modifier(ThemedBackground(grouped: true))
+        .overlay {
+            if progressIndicator {
+                ProgressView().scaleEffect(2)
+            }
+        }
     }
 
     private func databaseAlert(_ alertItem: DatabaseAlert) -> Alert {