Modernize MQTT discovery compatibility and runtime refreshes.

Align ArduinoHA with current Home Assistant MQTT discovery expectations by adding default entity IDs, device discovery support, safer runtime discovery refresh behavior, expanded entity category coverage, and the tests/docs needed to support the migration away from legacy object_id payloads.

README.md

@@ -20,6 +20,23 @@ but I successfully use it on ESP8266/ESP8255 boards in my projects.
 * Doxygen documentation for all classes
 * Covered by unit tests (AUnit + EpoxyDuino + AUniter)
 
+## Discovery Notes
+
+ArduinoHA supports two MQTT discovery modes:
+
+* Single-component discovery, which remains the default behavior and publishes one retained discovery payload per entity.
+* Device discovery, which can be enabled explicitly with `HAMqtt::enableDeviceDiscovery()` and publishes a single retained `homeassistant/device/.../config` payload with component mappings under `cmps`.
+
+For entity ID suggestions in Home Assistant, prefer `setDefaultEntityId()` over `setObjectId()`.
+`setObjectId()` is still available as a legacy fallback, but newer Home Assistant versions are moving toward `default_entity_id`.
+
+If you need to manage discovery at runtime:
+
+* Use `HABaseDeviceType::republishDiscovery()` after changing discovery-relevant config at runtime.
+* Use `HABaseDeviceType::removeFromDiscovery()` to clear the retained discovery payload for a single entity.
+
+When device discovery mode is enabled, runtime discovery refreshes automatically clear any stale retained per-entity config before republishing the device discovery payload.
+
 ## Supported HA types
 
 | Home Assistant type | Supported |
@@ -47,7 +64,7 @@ but I successfully use it on ESP8266/ESP8255 boards in my projects.
 | Switch              |     ✅     |
 | Update              |     ❌     |
 | Tag scanner         |     ✅     |
-| Text                |     ❌     |
+| Text                |     ✅     |
 | Vacuum              |     ❌     |
 | Valve               |     ❌     |
 | Water heater        |     ❌     |