Add MQTT monitor with Home Assistant autodiscovery

Poll lifepo4wered-cli every 30s (configurable), publish all registers as
one JSON state payload, and announce sensors/binary sensor via MQTT
discovery. run.sh pulls broker credentials from the Supervisor mqtt
service (Mosquitto addon) with manual overrides in addon options.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/stubs/paho/mqtt/client.py

@@ -0,0 +1,41 @@
+"""Minimal paho-mqtt stand-in for end-to-end smoke tests without a broker.
+
+Every publish is appended to the file named by $STUB_MQTT_LOG as
+"<topic>\t<payload>".
+"""
+
+import os
+
+
+class CallbackAPIVersion:
+    VERSION1 = 1
+    VERSION2 = 2
+
+
+class Client:
+    def __init__(self, *args, **kwargs):
+        self.on_connect = None
+        self._log = open(os.environ["STUB_MQTT_LOG"], "a")
+
+    def username_pw_set(self, username, password=None):
+        pass
+
+    def will_set(self, topic, payload=None, qos=0, retain=False):
+        pass
+
+    def connect(self, host, port=1883, keepalive=60):
+        pass
+
+    def loop_start(self):
+        if self.on_connect:
+            self.on_connect(self, None, {}, 0, None)
+
+    def loop_stop(self):
+        pass
+
+    def disconnect(self):
+        self._log.close()
+
+    def publish(self, topic, payload=None, qos=0, retain=False):
+        self._log.write("%s\t%s\n" % (topic, payload))
+        self._log.flush()