fix vue cli-service feature flag warning

ui/vue.config.js

@@ -1,4 +1,5 @@
 const { defineConfig } = require("@vue/cli-service");
+const webpack = require("webpack");
 
 module.exports = defineConfig({
   transpileDependencies: true,
@@ -11,4 +12,14 @@ module.exports = defineConfig({
       title: "Kalender-Gewinnspiel",
     },
   },
+  // https://stackoverflow.com/a/77765007
+  configureWebpack: {
+    plugins: [
+      new webpack.DefinePlugin({
+        // Vue CLI is in maintenance mode, and probably won't merge my PR to fix this in their tooling
+        // https://github.com/vuejs/vue-cli/pull/7443
+        __VUE_PROD_HYDRATION_MISMATCH_DETAILS__: "false",
+      }),
+    ],
+  },
 });