fix(beszel): restore timePeriod cast and improve error visibility

- Restore timePeriod union cast to fix typecheck (TS2769)
- Clear live data on subscription error so error UI always shows
- Emit error when no integration is configured for live subscription
- Add error state to system select input when query fails

packages/api/src/router/widgets/beszel.ts

@@ -162,7 +162,10 @@ export const beszelRouter = createTRPCRouter({
         containerStats: BeszelContainerStatsRecord | null;
       }>((emit) => {
         const integration = ctx.integrations[0];
-        if (!integration) return () => {};
+        if (!integration) {
+          emit.error(new Error("No Beszel integration configured"));
+          return () => {};
+        }
 
         const abortController = new AbortController();