feat: add Home Assistant integration (REST tools + WebSocket gateway)

- Add ha_list_entities, ha_get_state, ha_call_service tools via REST API
- Add WebSocket gateway adapter for real-time state_changed event monitoring
- Support domain/entity filtering, cooldown, and auto-reconnect with backoff
- Use REST API for outbound notifications to avoid WS race condition
- Gate tool availability on HASS_TOKEN env var
- Add 82 unit tests covering real logic (filtering, payload building, event pipeline)

gateway/run.py

@@ -469,7 +469,14 @@ class GatewayRunner:
                 logger.warning("Slack: slack-bolt not installed. Run: pip install 'hermes-agent[slack]'")
                 return None
             return SlackAdapter(config)
-        
+
+        elif platform == Platform.HOMEASSISTANT:
+            from gateway.platforms.homeassistant import HomeAssistantAdapter, check_ha_requirements
+            if not check_ha_requirements():
+                logger.warning("HomeAssistant: aiohttp not installed or HASS_TOKEN not set")
+                return None
+            return HomeAssistantAdapter(config)
+
         return None
     
     def _is_user_authorized(self, source: SessionSource) -> bool: