refactor: align frontend ownership boundaries

Close audit gaps across API drift, query policy, UI, and tests.

src/shared/api/index.ts

@@ -1,2 +1,4 @@
 export { useAuthenticatedQuery } from "./authenticated-query";
 export { apiClient, apiQueryClient, configureAuthClient } from "./client";
+export type { paths } from "./generated/schema";
+export { apiErrorCode } from "./problem-details";