feat: 实现 Windows 可选字体包安装链

apps/desktop/electron-builder.config.cjs

@@ -5,6 +5,8 @@ const windowsIcon = path.resolve(
   __dirname,
   "../../logos/desktop/windows/app.ico"
 );
+const nsisInclude = process.env.MD_TO_PDF_NSIS_INCLUDE?.trim() ||
+  "build/installer.nsh";
 
 module.exports = {
   appId: "com.md-to-pdf.desktop",
@@ -71,7 +73,7 @@ module.exports = {
     installerIcon: windowsIcon,
     uninstallerIcon: windowsIcon,
     installerLanguages: ["zh_CN"],
-    include: "build/installer.nsh",
+    include: nsisInclude,
     artifactName: `md-to-pdf-${version}-x86_64-Setup.\${ext}`
   }
 };