fix: use SuperJSON for cache persistence and add null guards to all widgets

SuperJSON preserves Date/Map/Set types through the Redis cache round-trip,
fixing RangeError crashes from date formatting. Added defensive null/undefined
guards across all widget components to handle useQuery loading states and
potential cache shape mismatches.

apps/nextjs/src/app/[locale]/boards/(content)/_creator.tsx

@@ -7,6 +7,7 @@ import "~/styles/gridstack.scss";
 
 import { dehydrate, HydrationBoundary } from "@tanstack/react-query";
 import type { PersistedClient } from "@tanstack/react-query-persist-client";
+import SuperJSON from "superjson";
 import { getQueryClient } from "@homarr/api/server";
 import { IntegrationProvider } from "@homarr/auth/client";
 import { auth } from "@homarr/auth/next";
@@ -121,7 +122,7 @@ async function QueryCacheHydration({ userId, boardId }: { userId: string; boardI
     const serialized = await getQueryCacheAsync(userId, boardId);
     if (!serialized) return null;
 
-    const persisted = JSON.parse(serialized) as PersistedClient;
+    const persisted = SuperJSON.parse<PersistedClient>(serialized);
     if (!persisted?.clientState?.queries?.length) return null;
 
     return <HydrationBoundary state={persisted.clientState} />;