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/widgets/src/clock/use-current-time.ts

@@ -1,4 +1,27 @@
-import { useWidgetNow } from "../common/use-widget-now";
+import { useEffect, useMemo, useRef, useState } from "react";
+import dayjs from "dayjs";
 
-export const useCurrentTime = ({ showSeconds }: { showSeconds: boolean }) =>
-  useWidgetNow(showSeconds ? "second" : "minute");
+export const useCurrentTime = ({ showSeconds }: { showSeconds: boolean }) => {
+  const [time, setTime] = useState<Date | null>(null);
+  const timeoutRef = useRef<ReturnType<typeof setTimeout>>(null);
+  const intervalRef = useRef<ReturnType<typeof setInterval>>(null);
+  const intervalMultiplier = useMemo(() => (showSeconds ? 1 : 60), [showSeconds]);
+
+  useEffect(() => {
+    setTime(new Date());
+    timeoutRef.current = setTimeout(
+      () => {
+        setTime(new Date());
+        intervalRef.current = setInterval(() => setTime(new Date()), intervalMultiplier * 1000);
+      },
+      intervalMultiplier * 1000 - (1000 * (showSeconds ? 0 : dayjs().second()) + dayjs().millisecond()),
+    );
+
+    return () => {
+      if (timeoutRef.current) clearTimeout(timeoutRef.current);
+      if (intervalRef.current) clearInterval(intervalRef.current);
+    };
+  }, [intervalMultiplier, showSeconds]);
+
+  return time;
+};