feat(FN-2663): add cached update-check setting, APIs, and banner

- Add global updateCheckEnabled setting to core schema/types and wire dashboard command to cache update checks in the CLI
- Implement dashboard server update-check cache module plus REST routes for status and refresh behavior
- Add dashboard client hook, legacy API helpers, and UpdateAvailableBanner UI to show cached CLI update notices
- Cover update-check server routes, hook behavior, banner rendering, and route registration with focused tests
- Document update-check configuration and API behavior in architecture and settings reference docs

packages/dashboard/app/components/UpdateAvailableBanner.tsx

@@ -0,0 +1,35 @@
+import "./UpdateAvailableBanner.css";
+import { X } from "lucide-react";
+
+interface UpdateAvailableBannerProps {
+  latestVersion: string;
+  currentVersion: string;
+  onDismiss: () => void;
+}
+
+export function UpdateAvailableBanner({ latestVersion, currentVersion, onDismiss }: UpdateAvailableBannerProps) {
+  return (
+    <div className="update-available-banner" role="status" aria-live="polite">
+      <p className="update-available-banner__text">
+        Update available: v{latestVersion} (current: v{currentVersion}). Run <code>npm i -g @runfusion/fusion</code> to
+        update. {" "}
+        <a
+          className="update-available-banner__link"
+          href="https://github.com/Runfusion/Fusion/releases"
+          target="_blank"
+          rel="noreferrer"
+        >
+          Release notes
+        </a>
+      </p>
+      <button
+        type="button"
+        className="update-available-banner__dismiss touch-target"
+        aria-label="Dismiss update notice"
+        onClick={onDismiss}
+      >
+        <X size={16} aria-hidden="true" />
+      </button>
+    </div>
+  );
+}