fix(beszel): harden cache layer and prevent blank widgets (#6052)

* fix(beszel): harden cache layer and prevent blank widgets

- Add debug logging across Beszel integration, request handler, and tRPC
  router (auth, fetch, SSE, per-procedure entry/exit) gated behind
  LOG_LEVEL=debug
- cached-request-handler: retry with backoff, isValid predicate to skip
  caching invalid data, in-flight dedup (single-flight per channel) to
  avoid thundering herd after cache invalidation
- redis channel: set-then-publish so storage is always consistent even
  when pubsub publish fails
- Beszel handlers: opt into fallbackToStaleOnError and retry so brief
  upstream hiccups don't throw away good cached data
- beszel-system-stats: add refetchInterval matching each time period's
  cache TTL so historical charts refresh in the background
- tRPC router: switch Promise.all -> Promise.allSettled for getSystems
  and getAlerts; getSystemStats returns an error object instead of
  throwing. Each result carries an optional error field so one failed
  integration no longer nukes the whole widget
- Widgets: add explicit isPending loader, empty state for grid and
  stats, and a shared per-integration error indicator (tooltip with
  failed integration names). Alerts and table now only show their
  empty state after loading completes
- Translation: add empty.noSystems key to beszelSystemGrid and
  beszelSystemStats

Addresses #6030

* style: auto-fix lint and format

---------

Co-authored-by: ajnart <ajnart@users.noreply.github.com>

packages/widgets/src/beszel/_shared/error-indicator.tsx

@@ -0,0 +1,25 @@
+"use client";
+
+import { Tooltip } from "@mantine/core";
+import { IconAlertTriangle } from "@tabler/icons-react";
+
+interface IntegrationResult {
+  integrationId: string;
+  integrationName?: string;
+  error?: string;
+}
+
+interface BeszelIntegrationErrorIndicatorProps {
+  results: IntegrationResult[];
+}
+
+export function BeszelIntegrationErrorIndicator({ results }: BeszelIntegrationErrorIndicatorProps) {
+  const failed = results.filter((r) => "error" in r && r.error);
+  if (failed.length === 0) return null;
+  const label = failed.map((r) => r.integrationName ?? r.integrationId).join(", ");
+  return (
+    <Tooltip label={label} position="left" withArrow>
+      <IconAlertTriangle size={14} color="var(--mantine-color-orange-6)" style={{ cursor: "help", flexShrink: 0 }} />
+    </Tooltip>
+  );
+}