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/__tests__/UpdateAvailableBanner.test.tsx

@@ -0,0 +1,50 @@
+import { describe, it, expect, vi } from "vitest";
+import { fireEvent, render, screen } from "@testing-library/react";
+import { useState } from "react";
+import { UpdateAvailableBanner } from "../UpdateAvailableBanner";
+
+describe("UpdateAvailableBanner", () => {
+  it("renders version information and release notes link", () => {
+    render(
+      <UpdateAvailableBanner latestVersion="0.7.0" currentVersion="0.6.0" onDismiss={vi.fn()} />,
+    );
+
+    expect(screen.getByText(/Update available: v0.7.0 \(current: v0.6.0\)/)).toBeInTheDocument();
+    expect(screen.getByText("npm i -g @runfusion/fusion")).toBeInTheDocument();
+    expect(screen.getByRole("link", { name: "Release notes" })).toHaveAttribute(
+      "href",
+      "https://github.com/Runfusion/Fusion/releases",
+    );
+  });
+
+  it("dismiss button calls onDismiss", () => {
+    const onDismiss = vi.fn();
+
+    render(
+      <UpdateAvailableBanner latestVersion="0.7.0" currentVersion="0.6.0" onDismiss={onDismiss} />,
+    );
+
+    fireEvent.click(screen.getByRole("button", { name: "Dismiss update notice" }));
+    expect(onDismiss).toHaveBeenCalledTimes(1);
+  });
+
+  it("can be hidden by parent on dismiss", () => {
+    function Harness() {
+      const [visible, setVisible] = useState(true);
+      if (!visible) return null;
+      return (
+        <UpdateAvailableBanner
+          latestVersion="0.7.0"
+          currentVersion="0.6.0"
+          onDismiss={() => setVisible(false)}
+        />
+      );
+    }
+
+    render(<Harness />);
+    expect(screen.getByRole("status")).toBeInTheDocument();
+
+    fireEvent.click(screen.getByRole("button", { name: "Dismiss update notice" }));
+    expect(screen.queryByRole("status")).toBeNull();
+  });
+});