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/scripts/merge-i18n-fragments.mjs

@@ -0,0 +1,43 @@
+import { readFileSync, writeFileSync, readdirSync } from 'node:fs';
+import { resolve, dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const root = resolve(dirname(fileURLToPath(import.meta.url)), '..');
+const fragmentsDir = resolve(root, 'messages/fragments');
+
+function deepMerge(target, source) {
+  for (const [key, value] of Object.entries(source)) {
+    if (
+      value &&
+      typeof value === 'object' &&
+      !Array.isArray(value) &&
+      target[key] &&
+      typeof target[key] === 'object' &&
+      !Array.isArray(target[key])
+    ) {
+      deepMerge(target[key], value);
+    } else {
+      target[key] = value;
+    }
+  }
+  return target;
+}
+
+function mergeLocale(locale) {
+  const mainPath = resolve(root, `messages/${locale}.json`);
+  const data = JSON.parse(readFileSync(mainPath, 'utf8'));
+  const suffix = `.${locale}.json`;
+  for (const name of readdirSync(fragmentsDir).sort()) {
+    if (!name.endsWith(suffix)) continue;
+    const frag = JSON.parse(
+      readFileSync(resolve(fragmentsDir, name), 'utf8'),
+    );
+    deepMerge(data, frag);
+    console.log(`merged ${name}`);
+  }
+  writeFileSync(mainPath, `${JSON.stringify(data, null, 2)}\n`);
+}
+
+mergeLocale('zh-CN');
+mergeLocale('en');
+console.log('fragments merged');