fix(updater): keep auto-updater alive across watcher restarts (v0.4.1)

Saving the Settings dialog calls _restart_watcher, which set+replaced the
shared stop_event the updater loop also keyed off — so a settings save
silently killed the auto-updater thread (race: survived one save, died on
the next). Heartbeats kept flowing but the agent stopped checking for /
applying updates until relaunch.

Give the updater its own app-lifetime event (_app_stop), set only on
Exit / when applying an update and untouched by watcher restarts. Adds
test_thor_tray.py (4 lifecycle tests). Bump to v0.4.1.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

thor_tray.py

@@ -1,5 +1,5 @@
 """
-Thor Watcher — System Tray Launcher  v0.4.0
+Thor Watcher — System Tray Launcher  v0.4.1
 Requires: pystray, Pillow, tkinter (stdlib)
 
 Run with:  pythonw thor_tray.py   (no console window)
@@ -334,7 +334,8 @@ def _show_cancel_message():
 class WatcherTray:
     def __init__(self):
         self.state = {}
-        self.stop_event = threading.Event()
+        self.stop_event = threading.Event()   # watcher lifecycle; replaced on restart
+        self._app_stop = threading.Event()    # app lifetime; only set on exit/update
         self._watcher_thread = None
         self._icon = None
         self._menu_lock = threading.Lock()
@@ -390,6 +391,7 @@ class WatcherTray:
                 subprocess.Popen(["explorer", HERE])
 
     def _exit(self, icon, item):
+        self._app_stop.set()
         self.stop_event.set()
         icon.stop()
 
@@ -478,7 +480,7 @@ class WatcherTray:
         # line in the log soon after startup; subsequent checks every ~5 min.
         update_check_counter = 27
 
-        while not self.stop_event.is_set():
+        while not self._app_stop.is_set():
             icon_status = self._tray_status()
 
             if self._icon is not None:
@@ -504,7 +506,7 @@ class WatcherTray:
                     self._do_update(url)
                     return
 
-            self.stop_event.wait(timeout=10)
+            self._app_stop.wait(timeout=10)
 
     def _do_update(self, download_url=None):
         """Notify tray then apply update. If url is None, fetch it first."""
@@ -519,6 +521,7 @@ class WatcherTray:
 
         success = apply_update(download_url)
         if success:
+            self._app_stop.set()
             self.stop_event.set()
             if self._icon is not None:
                 self._icon.stop()