fix: reliable Mudfish removal on plugin uninstall

Decky 3.3 often SIGKILLs plugins 5s after SIGTERM because its socket
listener spins on EOF and starves the event loop (seen for several
plugins). So:
- _unload/_uninstall run synchronously (an awaited worker thread could
  never resume), and the daemon stop no longer waits.
- A transient systemd path unit watches the plugins folder; if this
  plugin's folder stays gone for 20s it stops the daemon and deletes
  /opt/mudfish and the plugin settings, then removes itself.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.py

@@ -73,13 +73,16 @@ class Plugin:
         controller = self._get_controller()
         # Bring up the idle launcher and sign in so nodes are listed. Never starts the tunnel.
         await asyncio.to_thread(controller.prepare)
+        # Clean up Mudfish if the plugin folder disappears (uninstall), even if Decky kills us first.
+        plugin_dir = os.path.dirname(os.path.abspath(__file__))
+        await asyncio.to_thread(system.ensure_cleanup_watcher, plugin_dir, decky.DECKY_PLUGIN_SETTINGS_DIR)
         decky.logger.info("Mudfish VPN plugin loaded")
         # Watch for sleep/resume even while the panel is closed; a resumed tunnel is turned off.
         # Also look for a newer Mudfish release now and then (the controller limits it to once a day).
         ticks = 0
         while True:
             try:
-                await asyncio.to_thread(controller.check_resume, system.sleep_offset())
+                controller.check_resume(system.sleep_offset())
                 if ticks % LATEST_POLL_TICKS == 0:
                     await asyncio.to_thread(controller.refresh_latest)
             except Exception as e:
@@ -87,11 +90,14 @@ class Plugin:
             ticks += 1
             await asyncio.sleep(RESUME_POLL_SECONDS)
 
+    # _unload/_uninstall run synchronously on purpose: Decky closes the plugin socket right after
+    # asking it to stop, and its listener then spins on EOF and starves the event loop, so an
+    # awaited worker thread would never resume and the plugin is SIGKILLed after 5 seconds.
     async def _unload(self):
-        await asyncio.to_thread(self._get_controller().shutdown)
+        self._get_controller().shutdown()
         decky.logger.info("Mudfish VPN plugin unloaded")
 
     async def _uninstall(self):
         # Removing the plugin removes Mudfish too (user decision): VPN off, daemon stopped, /opt/mudfish gone.
-        await asyncio.to_thread(self._get_controller().uninstall)
+        self._get_controller().uninstall()
         decky.logger.info("Mudfish removed with the plugin")