fix(fc2c-i): router falls back to memory history when no window (vitest)

frontend/src/router.js

@@ -1,4 +1,4 @@
-import { createRouter, createWebHistory } from 'vue-router'
+import { createRouter, createWebHistory, createMemoryHistory } from 'vue-router'
 import PlaceholderView from './views/PlaceholderView.vue'
 import SettingsView from './views/SettingsView.vue'
 import GalleryView from './views/GalleryView.vue'
@@ -28,8 +28,13 @@ const routes = [
   { path: '/downloads',     name: 'downloads',     component: PlaceholderView, meta: { title: 'Downloads'     } }
 ]
 
+// Browser uses HTML5 history; non-browser (Vitest/SSR) falls back to memory
+// history so the module is importable without `window`.
+const history =
+  typeof window !== 'undefined' ? createWebHistory() : createMemoryHistory()
+
 const router = createRouter({
-  history: createWebHistory(),
+  history,
   routes
 })