server: graceful Ctrl-C shutdown; HendiCtrl closes connection cleanly

On KeyboardInterrupt, brewpi.py cancels all asyncio tasks (letting
HeaterTask's `with device.open()` finally block run), then calls
heater.close() as belt-and-suspenders before closing the event loop.

On shutdown HeaterHendi.activate(False) now sets the switch to 0 instead
of disabling remote control, so the Hendi stays in remote mode at 0 W
rather than dropping back to its local panel state.  HendiCtrl.close()
does the same (setSwitch(0)) then closes the serial port.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/brewpi.py

@@ -190,4 +190,22 @@ if __name__ == '__main__':
 	threading.Thread(target=http_server.serve_forever, daemon=True).start()
 	print("Serving {} on http://0.0.0.0:{}".format(web_dir, args.http_port))
 
-	server.run_forever()
+	loop = asyncio.get_event_loop()
+	try:
+		loop.run_forever()
+	except KeyboardInterrupt:
+		print("\nShutting down...")
+	finally:
+		# Cancel all tasks so their finally blocks (e.g. HeaterTask's
+		# `with device.open()`) get a chance to run before we close the port.
+		pending = asyncio.all_tasks(loop)
+		for task in pending:
+			task.cancel()
+		if pending:
+			loop.run_until_complete(asyncio.gather(*pending, return_exceptions=True))
+		# Belt-and-suspenders: explicitly close the heater connection even if
+		# the task cleanup above failed to reach HeaterHendi.activate(False).
+		heater.close()
+		http_server.shutdown()
+		loop.close()
+		print("Server stopped.")