refactor: split flat core into capability packages, layer the conversations service, English defaults for every model-facing text

src/beaver_gateway/frontends/mcp_server.py

@@ -45,10 +45,10 @@ from starlette.applications import Starlette
 from starlette.responses import HTMLResponse, JSONResponse, StreamingResponse
 from starlette.routing import Route
 
-from beaver_gateway.core import audit
-from beaver_gateway.frontends._urls import external_base
 from beaver_gateway.frontends.base import Frontend
+from beaver_gateway.frontends.urls import external_base
 from beaver_gateway.mcp.internal_app import ALL_NAMESPACE
+from beaver_gateway.security import audit
 
 if TYPE_CHECKING:
     from collections.abc import AsyncIterator, Mapping