Refactor project structure and enhance backend integration

- Expanded package inclusion in `pyproject.toml` to support new modules.
- Introduced new `adapters` and `protocol` packages for better organization.
- Added backend adapter implementations for control plane integration.
- Updated main application imports to reflect new package structure.
- Removed deprecated core components and adjusted documentation accordingly.
- Enhanced architecture documentation to clarify the new runtime and integration layers.

engine/app/main.py

@@ -20,11 +20,11 @@ except ImportError:
     logger.warning("aiortc not available - WebRTC endpoint will be disabled")
 
 from app.config import settings
-from app.backend_adapters import build_backend_adapter_from_settings
-from core.transports import SocketTransport, WebRtcTransport, BaseTransport
-from core.session import Session
+from adapters.control_plane.backend import build_backend_adapter_from_settings
+from runtime.transports import SocketTransport, WebRtcTransport, BaseTransport
+from runtime.session.manager import Session
 from processors.tracks import Resampled16kTrack
-from core.events import get_event_bus, reset_event_bus
+from runtime.events import get_event_bus, reset_event_bus
 
 # Check interval for heartbeat/timeout (seconds)
 _HEARTBEAT_CHECK_INTERVAL_SEC = 5