fix MQTT disconnect reason code comparison bug

The mypy fixes introduced a bug where disconnect callback was comparing
reason_code == 0 instead of reason_value == 0. Since reason_code is a
ReasonCode object, it never equals integer 0, causing clean disconnects
to never be detected and infinite retry loops to occur.

Fixed by using reason_value (extracted from reason_code.value) for
numeric comparison, consistent with how we extract the value for logging.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

frigate/comms/mqtt.py

@@ -244,7 +244,7 @@ class MqttClient(Communicator):
             logger.error("MQTT not reconnecting - stop flag set")
             return
 
-        if reason_code == 0:
+        if reason_value == 0:
             logger.error("MQTT not reconnecting - clean disconnect (code 0)")
             return