feat(frontend): 控制台 next-intl 中英双语

接入无 URL 前缀的 zh-CN/en，顶栏与外观设置可切换语言；选择写入 cookie 后刷新生效。

frontend/package.json

@@ -11,7 +11,8 @@
     "start": "next start -p 3010",
     "lint": "eslint",
     "format": "biome format --write .",
-    "format:check": "biome format ."
+    "format:check": "biome format .",
+    "check:i18n": "node scripts/check-i18n-keys.mjs"
   },
   "dependencies": {
     "@codemirror/lang-html": "^6.4.12",
@@ -63,6 +64,7 @@
     "lucide-react": "^1.28.0",
     "motion": "^12.43.0",
     "next": "16.3.0",
+    "next-intl": "^4.13.6",
     "next-themes": "^0.4.6",
     "pinyin-match": "^1.2.10",
     "radix-ui": "^1.6.7",