refactor: align frontend ownership boundaries

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

src/shared/ui/StateView.tsx

@@ -1,4 +1,4 @@
-import { Button, Paper, Stack, Text, Title } from "@mantine/core";
+import { Paper, Stack, Text, Title } from "@mantine/core";
 import type { FC, ReactNode } from "react";
 
 type StateViewProps = {
@@ -23,4 +23,4 @@ const StateView: FC<StateViewProps> = (props) => {
 	);
 };
 
-export { Button, StateView };
+export { StateView };