Title: Access to Zigbee2MQTT base topic or integration context in automations
Body:
Hi everyone! 
I’d like to request a feature related to multi-instance Zigbee2MQTT setups in Home Assistant.
The problem
When running multiple Zigbee2MQTT instances (e.g., in separate buildings, zones, or coordinators), devices may have overlapping or similar entity names like:
binary_sensor.kitchen_water_leak
binary_sensor.kitchen_water_leak_2
But these entities belong to different Zigbee2MQTT integrations (with different base MQTT topics), and there’s currently no way in automations to detect or access which base topic a device is tied to.
This makes centralized automations extremely difficult to manage without hardcoding or duplicating logic.
Limitations today
- There is no way to get the base MQTT topic of a Zigbee2MQTT entity in automations.
- Accessing the area in templates is technically possible, but only if the entity has been manually assigned to an area — and this doesn’t reflect the actual Zigbee2MQTT instance or topic.
- There’s no built-in
device.zigbee2mqtt_topic,zigbee_instance, or similar metadata.
What would help
Allow templates in automations to access:
- The base MQTT topic an entity is linked to (e.g.
zigbee2mqtt_home1,zigbee2mqtt_home2) - Or an explicit Zigbee2MQTT instance ID
This metadata could be available via device_attr(), state_attr(), or similar.
Workarounds today
Currently, we are forced to:
- Encode the Zigbee2MQTT topic in the entity name manually
- Duplicate automations for each instance
- Use naming conventions or assign custom attributes outside of HA
None of these scale well for dynamic or large deployments.
Suggested API or template additions
Something like this in templates would be ideal:
{{ device_attr(trigger.entity_id, 'zigbee2mqtt_topic') }}
This would make multi-hub setups much more powerful and allow truly reusable, scalable automations.
Thanks for considering!