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

tests/test_auth_query_token.py

@@ -7,8 +7,8 @@ import pytest
 from fastapi import HTTPException
 from starlette.requests import Request
 
-from beaver_gateway.core.auth import TokenStore
-from beaver_gateway.frontends._auth import require_token
+from beaver_gateway.security.auth import TokenStore
+from beaver_gateway.frontends.bearer import require_token
 
 
 def _request(query: str = "", headers: dict[str, str] | None = None) -> Request:
@@ -61,7 +61,7 @@ async def test_bootstrap_entry_can_carry_a_scope() -> None:
 
 
 def test_access_log_filter_masks_query_tokens() -> None:
-    from beaver_gateway.core.redact import RedactFilter
+    from beaver_gateway.security.redact import RedactFilter
 
     record = logging.LogRecord(
         "uvicorn.access",