feat(ui): implement save directory browse button and pre-detection check

- Add a 'Browse...' button to the Connection Status panel in StatusTab.qml.
- Check if save directory is set before wafer detection in HomePage.qml, prompting the user if empty.
- Resolve QML Connections warning by renaming onLogMessageEmitted to onLogMessage.
- Remove temporary debug stack traces from device_controller.py.

src/pygui/backend/controllers/device_controller.py

@@ -90,6 +90,10 @@ class DeviceController(QObject):
         self._detectFinished.connect(self._handle_detect_finished, Qt.ConnectionType.QueuedConnection)
         self._readFinished.connect(self._handle_read_finished, Qt.ConnectionType.QueuedConnection)
 
+        root_logger = logging.getLogger()
+        root_logger.addHandler(QmlActivityLogHandler(self))
+        root_logger.setLevel(logging.INFO)
+
     # ---- Properties ----
     @Property(list, notify=portsUpdated)
     def availablePorts(self) -> list[str]:
@@ -538,3 +542,14 @@ class DeviceController(QObject):
             "runtime": info.runtime,
             "cycleCount": info.cycle_count,
         }
+
+class QmlActivityLogHandler(logging.Handler):
+    def __init__(self, controller: DeviceController) -> None:
+        super().__init__()
+        self._controller = controller
+    def emit(self, record: logging.LogRecord) -> None:
+        timestamp = datetime.now().strftime("%H:%M:%S")
+        level = record.levelname
+        message = record.getMessage()
+        msg = f"[{timestamp}] {level}: {message}"
+        self._controller._append_log(msg)