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)

model_tools.py

@@ -94,6 +94,7 @@ def _discover_tools():
         "tools.process_registry",
         "tools.send_message_tool",
         "tools.honcho_tools",
+        "tools.homeassistant_tool",
     ]
     import importlib
     for mod_name in _modules: