party-lock: use Docker SDK instead of docker kill CLI

The docker binary is not available inside the party-lock container,
so switch to the Python Docker SDK via unix socket.

infra/party-lock/party-lock.py

@@ -2,12 +2,15 @@
 # /// script
 # dependencies = [
 #   "paho-mqtt>=2.0",
+#   "docker>=7.0",
 # ]
 # ///
 
 import os
 import stat
+import time
 
+import docker
 import paho.mqtt.client as mqtt
 
 MQTT_HOST = os.environ.get("MQTT_HOST", "mosquitto")
@@ -25,7 +28,13 @@ def rebuild_acl():
         f.write("\n".join(lines) + "\n")
     os.chmod(ACL_PATH, stat.S_IRWXU)
     os.chown(ACL_PATH, 1883, 1883)
-    os.system("docker kill -s HUP mosquitto 2>/dev/null || true")
+    try:
+        dc = docker.DockerClient(base_url="unix://var/run/docker.sock")
+        mosq = dc.containers.get("mosquitto")
+        mosq.kill(signal="HUP")
+    except Exception:
+        pass
+    time.sleep(0.05)
 
 def on_message(client, userdata, msg):
     global locked