feat(FN-1072): add Electron desktop renderer integration

- Add Electron main-process IPC handlers and preload bridges for API proxying, window controls, update install, and platform lookup
- Introduce a desktop renderer entrypoint with DesktopWrapper and a custom frameless TitleBar component
- Add Electron-aware renderer utilities including API transport selection and hooks for runtime detection, auto-update events, and deep links
- Update dashboard header behavior for Electron mode and expand desktop tests across preload, transport, hooks, and title bar flows
- Document the desktop renderer architecture and update desktop package config/dependencies

packages/desktop/src/renderer/__tests__/useAutoUpdate.test.ts

@@ -0,0 +1,54 @@
+// @vitest-environment jsdom
+
+import { act, cleanup, renderHook } from "@testing-library/react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { useAutoUpdate } from "../hooks/useAutoUpdate";
+
+describe("useAutoUpdate", () => {
+  afterEach(() => {
+    cleanup();
+    window.electronAPI = undefined;
+    vi.clearAllMocks();
+  });
+
+  it("subscribes to update notifications and exposes update info", async () => {
+    let onUpdateAvailable: ((info: Record<string, unknown>) => void) | undefined;
+    const installUpdate = vi.fn().mockResolvedValue(undefined);
+
+    window.electronAPI = {
+      onUpdateAvailable: (callback) => {
+        onUpdateAvailable = callback;
+        return () => {
+          onUpdateAvailable = undefined;
+        };
+      },
+      installUpdate,
+    };
+
+    const { result } = renderHook(() => useAutoUpdate());
+
+    act(() => {
+      onUpdateAvailable?.({ version: "1.2.3" });
+    });
+
+    expect(result.current.updateAvailable).toBe(true);
+    expect(result.current.updateInfo).toEqual({ version: "1.2.3" });
+
+    await act(async () => {
+      await result.current.downloadAndInstall();
+    });
+
+    expect(installUpdate).toHaveBeenCalledTimes(1);
+  });
+
+  it("returns safe defaults when not running in Electron", async () => {
+    window.electronAPI = undefined;
+
+    const { result } = renderHook(() => useAutoUpdate());
+
+    expect(result.current.updateAvailable).toBe(false);
+    expect(result.current.updateInfo).toBeNull();
+
+    await expect(result.current.downloadAndInstall()).resolves.toBeUndefined();
+  });
+});