Clean up i18n: translate 404 page Chinese text and remove placeholder German locale

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/views/NotFound404.vue

@@ -6,9 +6,9 @@
   <main>
     <div class="container text-center pt-7 pb-12">
       <h2 class="mb-7">404</h2>
-      <p>您想找的頁面不存在</p>
-      <p class="mb-7">請重新確認搜尋的項目或是回到 Files 頁</p>
-      <router-link to="/files" class="btn btn-c-primary btn-lg">回到 Files 頁</router-link>
+      <p>The page you are looking for does not exist.</p>
+      <p class="mb-7">Please check the URL or go back to the Files page.</p>
+      <router-link to="/files" class="btn btn-c-primary btn-lg">Go to Files</router-link>
     </div>
   </main>
 </template>