fix(agent-core): keep the Codex login exports in the services barrel

The bare side-effect import is the only one in this barrel, and no test can
prove it survives bundling, so the DI registration could be dropped from the
shipped artifact. Keeping the plain re-exports leaves the registration provable.

Author: elkaix

packages/agent-core/src/services/index.ts

@@ -110,7 +110,12 @@ export {
   CodexLoginNotFoundError,
   CodexLoginInvalidCodeError,
 } from './codexLogin/codexLogin';
-import './codexLogin/codexLoginService';
+export {
+  CodexLoginFlow,
+  CodexLoginService,
+  pickDefaultModel,
+} from './codexLogin/codexLoginService';
+export type { CodexLoginDeps } from './codexLogin/codexLoginService';
 
 
 export {