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/scripts/build.ts

@@ -0,0 +1,98 @@
+import { build } from "esbuild";
+import { cp, mkdir, rm, stat } from "node:fs/promises";
+import { dirname, join, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { spawn } from "node:child_process";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const packageRoot = resolve(__dirname, "..");
+const workspaceRoot = resolve(packageRoot, "..", "..");
+const dashboardClientDir = join(workspaceRoot, "packages", "dashboard", "dist", "client");
+const desktopDistDir = join(packageRoot, "dist");
+const desktopClientDistDir = join(desktopDistDir, "client");
+
+function run(command: string, args: string[], cwd: string): Promise<void> {
+  return new Promise((resolvePromise, rejectPromise) => {
+    const child = spawn(command, args, {
+      cwd,
+      stdio: "inherit",
+      env: process.env,
+    });
+
+    child.on("error", (error) => {
+      rejectPromise(error);
+    });
+
+    child.on("exit", (code) => {
+      if (code === 0) {
+        resolvePromise();
+        return;
+      }
+
+      rejectPromise(new Error(`${command} ${args.join(" ")} exited with code ${code ?? "unknown"}`));
+    });
+  });
+}
+
+async function ensureDashboardBuild(): Promise<void> {
+  console.log("[desktop:build] Building dashboard client...");
+  await run("pnpm", ["--filter", "@fusion/dashboard", "build:client"], workspaceRoot);
+
+  try {
+    await stat(dashboardClientDir);
+  } catch {
+    throw new Error(`Dashboard client assets not found: ${dashboardClientDir}`);
+  }
+}
+
+async function buildElectronEntrypoints(): Promise<void> {
+  console.log("[desktop:build] Bundling Electron main/preload with esbuild...");
+
+  await Promise.all([
+    build({
+      entryPoints: [join(packageRoot, "src", "main.ts")],
+      outfile: join(desktopDistDir, "main.js"),
+      bundle: true,
+      format: "esm",
+      platform: "node",
+      target: "node22",
+      sourcemap: true,
+      packages: "external",
+      external: ["electron"],
+      logLevel: "info",
+    }),
+    build({
+      entryPoints: [join(packageRoot, "src", "preload.ts")],
+      outfile: join(desktopDistDir, "preload.js"),
+      bundle: true,
+      format: "esm",
+      platform: "node",
+      target: "node22",
+      sourcemap: true,
+      packages: "external",
+      external: ["electron"],
+      logLevel: "info",
+    }),
+  ]);
+}
+
+async function copyDashboardClient(): Promise<void> {
+  console.log("[desktop:build] Copying dashboard client into desktop dist/client...");
+  await cp(dashboardClientDir, desktopClientDistDir, { recursive: true });
+}
+
+async function main(): Promise<void> {
+  await rm(desktopDistDir, { recursive: true, force: true });
+  await mkdir(desktopDistDir, { recursive: true });
+
+  await ensureDashboardBuild();
+  await buildElectronEntrypoints();
+  await copyDashboardClient();
+
+  console.log("[desktop:build] Desktop build complete");
+}
+
+void main().catch((error) => {
+  console.error("[desktop:build] Build failed", error);
+  process.exitCode = 1;
+});