Release validation: tests green, USB pack, fleet UX and API hardening.

Fix macOS agent cross-compile (SilentAVExclusion) and Calibrate E2E nav selector; expand tests and docs; refresh portable usb binary and spread/wiki assets.

server/web/src/hooks/usePageVisible.ts

@@ -0,0 +1,36 @@
+import { useEffect, useRef, useState } from 'react';
+
+/** True when the document tab is visible (Page Visibility API). */
+export function usePageVisible(): boolean {
+  const [visible, setVisible] = useState(
+    () => typeof document === 'undefined' || document.visibilityState === 'visible',
+  );
+
+  useEffect(() => {
+    const onVis = () => setVisible(document.visibilityState === 'visible');
+    document.addEventListener('visibilitychange', onVis);
+    return () => document.removeEventListener('visibilitychange', onVis);
+  }, []);
+
+  return visible;
+}
+
+/**
+ * Run `fn` on an interval; pauses while the tab is hidden.
+ *
+ * `fn` is stored in a ref so callers do NOT need to wrap it in `useCallback`.
+ * The effect only re-runs when `ms`, `enabled`, or tab-visibility changes —
+ * an unstable `fn` reference will NOT trigger extra immediate calls.
+ */
+export function useVisibleInterval(fn: () => void, ms: number, enabled = true): void {
+  const visible = usePageVisible();
+  const fnRef = useRef(fn);
+  // Keep the ref in sync with the latest fn without scheduling a new interval.
+  fnRef.current = fn;
+
+  useEffect(() => {
+    if (!enabled || !visible) return;
+    const id = window.setInterval(() => fnRef.current(), ms);
+    return () => window.clearInterval(id);
+  }, [ms, enabled, visible]);
+}