perf: frontend request cache, poll pause, and code-split shell (#1052)

Host/status caching, shell code-split, SSH pool waits, host-metrics concurrency, background-tab idle, per-host status subscriptions, homepage poll quieting, and virtualized host sidebar + file manager lists.

src/ui/features/homepage/widgets/RecentActivityWidget.tsx

@@ -18,6 +18,7 @@ import { GRID_SIZE } from "@/types/homepage-types";
 import { getRecentActivity } from "@/api/dashboard-api";
 import type { RecentActivityItem } from "@/api/dashboard-api";
 import { WidgetTitle } from "./WidgetTitle";
+import { runVisibleInterval } from "../use-visible-interval";
 
 function relativeTime(ts: string): string {
   const diff = Date.now() - new Date(ts).getTime();
@@ -75,8 +76,9 @@ function RecentActivityWidget({
 
   useEffect(() => {
     fetchData();
-    const iv = setInterval(fetchData, 60_000);
-    return () => clearInterval(iv);
+    return runVisibleInterval(() => {
+      void fetchData();
+    }, 60_000);
   }, [maxItems, filterTypes.join(",")]);
 
   if (loading) {