fix: QThread crash on iPod connect and device detection — proper wait() lifecycle

Root cause: QThread C++ destructor ran while underlying OS thread was
still terminating. The pattern of checking isRunning() and using
short timeouts (wait(3000/5000)) left a window where the Python
reference was dropped and Shiboken destroyed the C++ object before
the thread fully exited.

Fixes:
- Remove all self.finished.connect(self.deleteLater) — unsafe,
  deleteLater from within run() or from worker thread races with
  thread termination
- _cleanup_worker: always call wait() (no timeout) before nulling
  the Python reference — guarantees OS thread is fully dead
- Add _is_worker_running() helper with try/except RuntimeError
  guard to safely check stale C++ objects
- DeviceMonitor._poll/stop/wait: use wait() with no timeout
- closeEvent: guard isRunning() with try/except RuntimeError

src/device_monitor.py

@@ -11,6 +11,9 @@ logger = logging.getLogger(__name__)
 class _DetectWorker(QThread):
     finished = pyqtSignal(object)
 
+    def __init__(self, parent=None):
+        super().__init__(parent)
+
     def run(self):
         try:
             devices = IPodDevice().detect_devices()
@@ -38,19 +41,29 @@ class DeviceMonitor(QObject):
 
     def stop(self):
         self.timer.stop()
-        if self._poll_worker and self._poll_worker.isRunning():
+        if self._poll_worker:
             self._poll_worker.quit()
-            self._poll_worker.wait(3000)
+            self._poll_worker.wait()
+            self._poll_worker = None
         self._device_ids.clear()
 
     def _poll(self):
-        if self._poll_worker and self._poll_worker.isRunning():
-            return
-        self._poll_worker = _DetectWorker()
-        self._poll_worker.finished.connect(self._on_devices_detected)
-        self._poll_worker.start()
+        if self._poll_worker:
+            try:
+                if self._poll_worker.isRunning():
+                    return
+            except RuntimeError:
+                self._poll_worker = None
+        worker = _DetectWorker()
+        worker.finished.connect(self._on_devices_detected)
+        worker.start()
+        self._poll_worker = worker
 
     def _on_devices_detected(self, devices):
+        if self._poll_worker:
+            self._poll_worker.quit()
+            self._poll_worker.wait()
+            self._poll_worker = None
         current_ids = {d["id"] for d in devices}
         if current_ids != self._device_ids:
             self._device_ids = current_ids