feat: add shared setup viewer with token detection and read-only mode

Detect ?share=token query param on setup detail page, fetch via
/api/shared/:token, and display read-only view with "Shared setup"
banner. Hide all owner controls (add items, share, delete, classification)
in shared view. Show "Link not available" error for invalid tokens.

Plan: 32-04 (Setup Sharing System - Shared Setup Viewer)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/hooks/useSetups.ts

@@ -74,6 +74,15 @@ export function usePublicSetup(setupId: number | null) {
 	});
 }
 
+export function useSharedSetup(token: string | null) {
+	return useQuery({
+		queryKey: ["shared-setup", token],
+		queryFn: () => apiGet<SetupWithItems>(`/api/shared/${token}`),
+		enabled: !!token,
+		retry: false,
+	});
+}
+
 export function useCreateSetup() {
 	const queryClient = useQueryClient();
 	return useMutation({