Refactor UI state management and improve error handling in the application. Added success and error messages to enhance user feedback during package creation and device connection status updates.

device.go

@@ -68,13 +68,18 @@ func (d *Device) Connect() error {
 
 // ExitDevMode sends the command to exit dev mode.
 func (d *Device) ExitDevMode() error {
-	if !d.Connected || d.Port == nil {
-		return fmt.Errorf("device not connected")
+	if d.Port == nil {
+		return fmt.Errorf("port not open")
 	}
 
-	// Send exit dev mode command
-	// TODO: Replace with the actual command sequence to exit dev mode
-	// This is currently not implemented on the Cardputer side.
+	// disable dev mode
+	_, err := d.Port.Write([]byte{0xAA, 0x05, 0x00, 0x00, 0x00})
+	if err != nil {
+		return fmt.Errorf("failed to send exit dev mode command: %w", err)
+	}
+
+	// Allow some time for the device to respond or settle if needed
+	time.Sleep(100 * time.Millisecond)
 
 	return nil
 }