feat(FN-5587): add windows desktop packaging workflow, scripts, and tests

Adds Windows desktop packaging support for Fusion, including a new GitHub Actions workflow for building Windows desktop targets, matching build scripts in the root and desktop package, a test for electron-builder configuration, and documentation of the packaging path.

Fusion-Task-Id: FN-5587

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>
Fusion-Task-Id: FN-5587

packages/desktop/src/__tests__/electron-builder-config.test.ts

@@ -0,0 +1,36 @@
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, expect, it } from "vitest";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const desktopRoot = path.resolve(__dirname, "../..");
+
+async function readDesktopFile(relativePath: string): Promise<string> {
+  return readFile(path.join(desktopRoot, relativePath), "utf-8");
+}
+
+describe("electron-builder windows config", () => {
+  it("keeps required Windows packaging targets and metadata", async () => {
+    const builderConfig = await readDesktopFile("electron-builder.yml");
+
+    expect(builderConfig).toContain("win:");
+    expect(builderConfig).toMatch(/win:\s*[\s\S]*?target:\s*[\s\S]*?-\s*target:\s*nsis/m);
+    expect(builderConfig).toMatch(/win:\s*[\s\S]*?target:\s*[\s\S]*?-\s*target:\s*portable/m);
+
+    expect(builderConfig).toMatch(/nsis:\s*[\s\S]*?oneClick:\s*false/m);
+    expect(builderConfig).toMatch(/nsis:\s*[\s\S]*?allowToChangeInstallationDirectory:\s*true/m);
+
+    expect(builderConfig).toMatch(/artifactName:\s*"\$\{productName\}-\$\{version\}-\$\{os\}-\$\{arch\}\.\$\{ext\}"/m);
+    expect(builderConfig).toMatch(/appId:\s*com\.gsxdsm\.fusion\.desktop/m);
+    expect(builderConfig).toMatch(/productName:\s*Fusion/m);
+  });
+
+  it("exposes a dedicated dist:win script", async () => {
+    const packageJsonRaw = await readDesktopFile("package.json");
+    const packageJson = JSON.parse(packageJsonRaw) as { scripts?: Record<string, string> };
+
+    expect(packageJson.scripts?.["dist:win"]).toBe("electron-builder --win");
+  });
+});