feat(FN-1073): add desktop CLI workflow and packaging support

- Add new `fn desktop` CLI command with argument handling and comprehensive command/bin tests
- Implement desktop build and hot-reload dev scripts and wire package scripts/dependencies for Electron workflows
- Add electron-builder configuration and desktop main-process/integration test coverage to stabilize packaging behavior
- Document desktop development and usage in README files and include a changeset for the published CLI package

packages/desktop/src/main.ts

@@ -1,6 +1,6 @@
 import { app, BrowserWindow, nativeImage, Tray } from "electron";
 import { join, resolve } from "node:path";
-import { fileURLToPath } from "node:url";
+import { fileURLToPath, pathToFileURL } from "node:url";
 import { setupDeepLinkHandler, registerDeepLinkProtocol } from "./deep-link.js";
 import { registerIpcHandlers } from "./ipc.js";
 import { buildAppMenu } from "./menu.js";
@@ -17,11 +17,33 @@ interface AppWithQuitFlag {
   isQuitting?: boolean;
 }
 
+const DEFAULT_DEV_DASHBOARD_URL = "http://localhost:5173";
+
+function isDevelopmentMode(): boolean {
+  return process.env.NODE_ENV === "development" || process.argv.includes("--dev");
+}
+
+const PRODUCTION_DASHBOARD_URL = pathToFileURL(
+  join(import.meta.dirname, "client", "index.html"),
+).toString();
+
+export const IS_DEVELOPMENT = isDevelopmentMode();
+export const DASHBOARD_URL = process.env.FUSION_DASHBOARD_URL ?? (
+  IS_DEVELOPMENT ? DEFAULT_DEV_DASHBOARD_URL : PRODUCTION_DASHBOARD_URL
+);
+
+function enableSourceMaps(): void {
+  const processWithSourceMaps = process as NodeJS.Process & {
+    setSourceMapsEnabled?: (enabled: boolean) => void;
+  };
+  processWithSourceMaps.setSourceMapsEnabled?.(true);
+}
+
+enableSourceMaps();
+
 let mainWindow: BrowserWindow | null = null;
 let tray: Tray | null = null;
 
-export const DASHBOARD_URL = process.env.FUSION_DASHBOARD_URL || "http://localhost:4040";
-
 function getAppWithQuitFlag(): Electron.App & AppWithQuitFlag {
   return app as Electron.App & AppWithQuitFlag;
 }
@@ -35,7 +57,7 @@ export function createMainWindow(state?: WindowState): BrowserWindow {
     ...(hasValidPosition ? { x: state.x, y: state.y } : {}),
     title: "Fusion",
     webPreferences: {
-      preload: join(import.meta.dirname, "preload.ts"),
+      preload: join(import.meta.dirname, "preload.js"),
       contextIsolation: true,
       nodeIntegration: false,
     },