refactor: drop server-seeded widget clock

The WidgetTimeProvider plumbed a server timestamp and the container's
timezone down to useWidgetNow so clock widgets would paint a real time in
the SSR HTML instead of "--:--". That traded a cosmetic first-paint win for
a wrong clock: the seeded timezone is the server's, so anyone whose timezone
differs from the container's saw an incorrect time for the whole hydration
window. Fixing that properly needs a client-set timezone cookie read during
RSC render, which is far more plumbing than the problem warrants.

Revert the clock to release/v2 behaviour ("--:--" until hydration) and drop
the provider, the @homarr/widgets/time export and their tests. The e2e clock
assertions now wait on hydration explicitly instead of the seeded paint.

Also restore the widget.beszel.getSystemStats persistence exclusion. #6289
added it deliberately to keep those large time-series payloads out of the
persisted cache, and this branch had removed it with no stated rationale.

Query-cache persistence and the background-refresh indicator are unchanged.

packages/api/src/query-cache.ts

@@ -8,7 +8,9 @@ export const queryCacheDefaultGcTimeMs = 1000 * 60 * 5;
 export const queryCacheMetadataStaleTimeMs = 1000 * 60 * 5;
 
 const widgetDataQueryPaths = new Set(["app.byId", "app.byIds", "docker.getContainers", "integration.byIds"]);
-const excludedWidgetPaths = new Set(["widget.app.ping"]);
+// Beszel system stats are large time-series payloads and were deliberately kept out of
+// the persisted cache in #6289; live stats come from an SSE subscription instead.
+const excludedWidgetPaths = new Set(["widget.app.ping", "widget.beszel.getSystemStats"]);
 
 export const isWidgetDataTrpcPath = (path: string) => {
   if (path.startsWith("widget.")) return !excludedWidgetPaths.has(path);