Per-entity availability, deferred discovery publish, suggested precision

- Add HAAvailabilityConfig for per-entity availability_topic and payloads
- Defer discovery until MQTT connected; publish availability after discovery
- HASensor/HANumber: optional suggested_display_precision in discovery
- HASerializer/HADictionary: extend for new keys; update device types and mocks
- Docs and examples reflect availability and precision usage
- Tests updated for discovery and availability behavior
- Ignore .cursor/ in repo root

docs/device-and-discovery.md

@@ -13,6 +13,8 @@ Represents the physical board in Home Assistant: one device can expose multiple
 **Optional metadata** (each costs some RAM/flash; skip on tiny MCUs unless needed):
 
 - `setName`, `setSoftwareVersion`, `setManufacturer`, `setModel`, `setConfigurationUrl`
+- `setModelId`, `setHardwareVersion`, `setSerialNumber`, `setSuggestedArea`, `setViaDevice`
+- `addConnection("mac", "aa:bb:cc:dd:ee:ff")` or `setConnectionsJson("[[\"mac\",\"aa:bb:cc:dd:ee:ff\"]]")`
 
 String setters take **pointers whose contents are not copied** — use literals or storage that outlives the call.
 
@@ -41,8 +43,28 @@ mqtt.setDataPrefix("myDataPrefix");
 - **Default:** one retained discovery topic per entity (single-component discovery).
 - **Optional:** call `HAMqtt::enableDeviceDiscovery()` to publish a single **device** discovery payload with components under `cmps` (see project README for migration notes).
 
+Device discovery can also publish richer origin/device metadata, for example:
+
+```cpp
+device.setModelId("esp32-s3-devkit");
+device.setHardwareVersion("rev-b");
+device.setSerialNumber("SN-00042");
+device.setSuggestedArea("Garage");
+device.setViaDevice("main_gateway");
+device.addConnection("mac", "AA:BB:CC:DD:EE:FF");
+mqtt.setOriginSupportUrl("https://example.com/device-help");
+```
+
 For entity identifiers in Home Assistant, prefer **`setDefaultEntityId()`** over legacy **`setObjectId()`**.
 
+Common entity discovery metadata can be configured on most entity types via:
+
+- `setEnabledByDefault(bool)`
+- `setEntityPicture(const char*)`
+- `setQos(uint8_t)`
+- `setEncoding(const char*)`
+- `setEntityCategory(const char*)`
+
 ### Runtime discovery changes
 
 After changing discovery-related settings at runtime:

docs/mqtt-usage.md

@@ -46,12 +46,70 @@ mqtt.publish("customTopic", "payload", true);     // retained
 
 ```cpp
 device.enableSharedAvailability();
+device.setPayloadAvailable("up");
+device.setPayloadNotAvailable("down");
 device.enableLastWill();   // broker publishes offline when TCP drops
 // device.setAvailability(false);  // optional: start as offline
 ```
 
 **Per-entity availability:** call `someEntity.setAvailability(true/false)` on each type. Does not use LWT the same way as shared mode; see examples under `examples/availability/`.
 
+Custom per-entity payloads are supported:
+
+```cpp
+sensor.setPayloadAvailable("ready");
+sensor.setPayloadNotAvailable("lost");
+```
+
+For multi-topic availability discovery, add full MQTT topics and a mode:
+
+```cpp
+sensor.setAvailabilityMode("all");
+sensor.addAvailabilityEntry("bridge/status");
+sensor.addAvailabilityEntry("sensor/status", "{{ value_json.state }}");
+```
+
+## Discovery helpers by entity
+
+Common entity discovery metadata is available on most entity classes:
+
+```cpp
+entity.setEnabledByDefault(false);
+entity.setEntityPicture("https://example.com/entity.png");
+entity.setQos(1);
+entity.setEncoding("utf-8");
+entity.setEntityCategory("diagnostic");
+```
+
+Read-only sensor presentation/template helpers:
+
+```cpp
+sensor.setSuggestedDisplayPrecision(2);
+sensor.setValueTemplate("{{ value_json.temperature }}");
+sensor.setJsonAttributesTemplate("{{ value_json.attrs | tojson }}");
+sensor.setLastResetValueTemplate("{{ value_json.last_reset }}");
+sensor.setDeviceClass("enum");
+sensor.setOptions("idle;charging;discharging;fault");
+```
+
+Writable entity template/payload helpers:
+
+```cpp
+mySwitch.setPayloadOn("ENABLE");
+mySwitch.setPayloadOff("DISABLE");
+mySwitch.setStateOn("running");
+mySwitch.setStateOff("stopped");
+mySwitch.setValueTemplate("{{ value_json.state }}");
+mySwitch.setCommandTemplate("{{ value_json.command }}");
+
+myNumber.setPayloadReset("RESET");
+myNumber.setCommandTemplate("{{ value | float | round(1) }}");
+
+mySelect.setCommandTemplate("{{ value_json.choice }}");
+myText.setCommandTemplate("{{ value_json.text }}");
+myButton.setPayloadPress("PRESS");
+```
+
 ## Compiler macros
 
 Defined in `ArduinoHADefines.h` or via build flags.