refactor: align frontend ownership boundaries

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

src/shared/ui/index.ts

@@ -1,3 +1,3 @@
 export { AppShell } from "./AppShell";
 export { LoadingSkeleton } from "./LoadingSkeleton";
-export { Button, StateView } from "./StateView";
+export { StateView } from "./StateView";