feat: HA Discovery protocol handler for auto-registering devices

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/test_discovery.py

@@ -0,0 +1,78 @@
+import json
+import pytest
+from unittest.mock import AsyncMock
+
+from mqtt_home.discovery import parse_discovery_topic, handle_discovery_message
+from mqtt_home.config import Settings
+from mqtt_home.mqtt_client import MqttClient
+
+
+@pytest.fixture
+def settings():
+    return Settings(
+        mqtt_host="localhost",
+        emqx_api_url="http://localhost:18083/api/v5",
+        emqx_api_key="test-key",
+        emqx_api_secret="test-secret",
+        database_url="sqlite+aiosqlite:///:memory:",
+    )
+
+
+def test_parse_discovery_topic_valid():
+    result = parse_discovery_topic("homeassistant/light/abc123/config")
+    assert result is not None
+    assert result["component"] == "light"
+    assert result["node_id"] == "abc123"
+
+
+def test_parse_discovery_topic_nested_node():
+    result = parse_discovery_topic("homeassistant/sensor/room/temperature/config")
+    assert result is not None
+    assert result["component"] == "sensor"
+    assert result["node_id"] == "room/temperature"
+
+
+def test_parse_discovery_topic_invalid():
+    assert parse_discovery_topic("other/topic/config") is None
+    assert parse_discovery_topic("homeassistant/light/abc") is None
+    assert parse_discovery_topic("homeassistant/light/abc/status") is None
+
+
+async def test_handle_discovery_creates_device(db_session, settings):
+    mqtt_client = MqttClient(settings)
+    mqtt_client.subscribe = AsyncMock()
+
+    payload = json.dumps({
+        "name": "客厅灯",
+        "state_topic": "home/living/light/status",
+        "command_topic": "home/living/light/set",
+        "device_class": "light",
+    })
+
+    device = await handle_discovery_message(
+        "homeassistant/light/living_room/config",
+        payload,
+        db_session,
+        mqtt_client,
+    )
+    assert device is not None
+    assert device.name == "客厅灯"
+    assert device.protocol == "ha_discovery"
+    assert device.mqtt_topic == "home/living/light/status"
+    mqtt_client.subscribe.assert_called_once_with("home/living/light/status", qos=1)
+
+
+async def test_handle_discovery_duplicate(db_session, settings):
+    mqtt_client = MqttClient(settings)
+    mqtt_client.subscribe = AsyncMock()
+
+    payload = json.dumps({
+        "name": "灯",
+        "state_topic": "home/light",
+    })
+
+    await handle_discovery_message("homeassistant/light/test/config", payload, db_session, mqtt_client)
+    device2 = await handle_discovery_message("homeassistant/light/test/config", payload, db_session, mqtt_client)
+    # Same discovery_topic should not create duplicate
+    assert device2 is not None
+    mqtt_client.subscribe.assert_called_once()  # Only called once