fix: guard UART window creation with try-except to prevent silent crash

On Windows the UartMonitorWindow could crash instantly without any
error message. Added try-except around window creation in _read_serial
so errors are logged instead of silently killing the window.

Also added empty port guard before attempting to open.

src/gui/main_window.py

@@ -1585,12 +1585,20 @@ class MainWindow(ctk.CTk):
 
     def _read_serial(self) -> None:
         """Open the UART Monitor window."""
-        port = self._port_var.get()
+        port = self._port_var.get().strip()
+        if not port:
+            self._log_message("  ✗ No serial port selected")
+            return
         baudrate = self._config.serial_baudrate if self._config else 115200
+        try:
             self._uart_window = UartMonitorWindow(
                 self, port=port, baudrate=baudrate,
                 on_log=self._log_message,
             )
+        except Exception as e:
+            self._log_message(f"  ✗ Failed to open UART window: {e}")
+            import traceback
+            self._log_message(traceback.format_exc())
 
     def _test_serial_version(self) -> None:
         """Test serial port by sending 'ver()' command and parsing response."""