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.

packages/widgets/src/speedtest-tracker/component.tsx

@@ -24,7 +24,7 @@ export default function SpeedtestTrackerWidget({ options, integrationIds }: Widg
         (acc, item) => ({
           latestResult: item.dashboard.latestResult ?? acc.latestResult,
           stats: mergeStats(acc.stats, item.dashboard.stats),
-          recentResults: [...acc.recentResults, ...item.dashboard.recentResults],
+          recentResults: [...acc.recentResults, ...(item.dashboard.recentResults ?? [])],
         }),
         { latestResult: null, stats: null, recentResults: [] },
       ),
@@ -32,7 +32,7 @@ export default function SpeedtestTrackerWidget({ options, integrationIds }: Widg
   );
 
   const twelveHoursAgo = Date.now() - 12 * 60 * 60 * 1000;
-  const recentFiltered = combined.recentResults.filter((result) => result.created_at.getTime() > twelveHoursAgo);
+  const recentFiltered = combined.recentResults.filter((result) => new Date(result.created_at).getTime() > twelveHoursAgo);
 
   const hasStatSection =
     (options.showLatestResult && combined.latestResult !== null) || (options.showStats && combined.stats !== null);