fix CI failing with Invalid value "iife" for option "worker.format"

UMD and IIFE output formats are not supported for code-splitting builds. see https://github.com/vitejs/vite/issues/18585

vite.config.ts

@@ -97,6 +97,9 @@ export default ({
         cert: fs.readFileSync("./backend/dev_tls_m.localhost.crt"),
       },
     },
+    worker: {
+      format: "es",
+    },
     build: {
       minify: mode === "production" ? true : false,
       sourcemap: true,