Register per-camera notifications MQTT callbacks (#23637)

* fix per-camera notification MQTT topics never being registered

register notifications/set and notifications/suspend callbacks for each camera, and gate the global notifications topics on per-camera config as well as global (matching WebPushClient creation in app.py). Unregistered topics were silently dropped by paho since only registered callbacks receive messages.

* add tests

frigate/comms/mqtt.py

@@ -41,6 +41,18 @@ class MqttClient(Communicator):
         self.publish("available", "stopped", retain=True)
         self.client.disconnect()
 
+    def _notifications_enabled_in_config(self) -> bool:
+        """Whether notifications are configured globally or on any camera.
+
+        Notifications can be enabled per camera with the global config left
+        disabled, so the global topics must consider both (matching how
+        app.py decides to create the WebPushClient).
+        """
+        return self.config.notifications.enabled_in_config or any(
+            cam.enabled and cam.notifications.enabled_in_config
+            for cam in self.config.cameras.values()
+        )
+
     def _set_initial_topics(self) -> None:
         """Set initial state topics."""
         for camera_name, camera in self.config.cameras.items():
@@ -157,7 +169,7 @@ class MqttClient(Communicator):
                     retain=True,
                 )
 
-        if self.config.notifications.enabled_in_config:
+        if self._notifications_enabled_in_config():
             self.publish(
                 "notifications/state",
                 "ON" if self.config.notifications.enabled else "OFF",
@@ -256,6 +268,7 @@ class MqttClient(Communicator):
             "review_detections",
             "object_descriptions",
             "review_descriptions",
+            "notifications",
         ]
 
         for name in self.config.cameras.keys():
@@ -265,6 +278,12 @@ class MqttClient(Communicator):
                     self.on_mqtt_command,
                 )
 
+            # notifications suspend doesn't follow the /set topic pattern
+            self.client.message_callback_add(
+                f"{self.mqtt_config.topic_prefix}/{name}/notifications/suspend",
+                self.on_mqtt_command,
+            )
+
             if self.config.cameras[name].onvif.host:
                 self.client.message_callback_add(
                     f"{self.mqtt_config.topic_prefix}/{name}/ptz",
@@ -289,7 +308,7 @@ class MqttClient(Communicator):
                     self.on_mqtt_command,
                 )
 
-        if self.config.notifications.enabled_in_config:
+        if self._notifications_enabled_in_config():
             self.client.message_callback_add(
                 f"{self.mqtt_config.topic_prefix}/notifications/set",
                 self.on_mqtt_command,