Add OnlineMode route and extract app styles

Introduce an OnlineMode route and placeholder component, wire it into the router and Home menu (replace the removed local-vs-bot entry). Rename utils/index.ts to router/index.ts and add the new /onlineMode route; update main.ts to import the router from ./router and include the new app.css. Extract shared #game and .game-content styles into GUI/src/app.css and remove the duplicate styles from LocalMode.vue. Make small UI tweaks: adjust GameEndedMenu width, minor formatting/attribute fixes in Layout.vue and LocalMode.vue.

GUI/src/router/index.ts

@@ -0,0 +1,29 @@
+import Home from '@/Home.vue'
+import NotFound from '@/NotFound.vue'
+import LocalMode from '@/routes/LocalMode.vue'
+import OnlineMode from '@/routes/OnlineMode.vue'
+import { createRouter, createWebHistory } from 'vue-router'
+
+const router = createRouter({
+  history: createWebHistory(import.meta.env.BASE_URL),
+  routes: [
+    {
+      path: '/',
+      name: 'Startseite',
+      component: Home,
+    },
+    {
+      path: "/localMode",
+      name: "LocalMode",
+      component: LocalMode
+    },
+    {
+      path: "/onlineMode",
+      name: "OnlineMode",
+      component: OnlineMode
+    },
+    { path: '/:pathMatch(.*)*', name: 'Nicht gefunden', component: NotFound },
+  ],
+})
+
+export default router