refactor: 完成全站国际化改造，统一多语言支持

此提交完成了全项目的国际化适配：
1. 新增多语言翻译文件与基础配置
2. 替换所有硬编码文本为i18n调用
3. 优化语言切换与文档语言同步逻辑
4. 重构部分业务逻辑以支持动态翻译
5. 移除过时代码与硬编码配置

src/i18n/index.ts

@@ -1,3 +1,5 @@
+"use client";
+
 import i18n from "i18next";
 import LanguageDetector from "i18next-browser-languagedetector";
 import { initReactI18next } from "react-i18next";
@@ -5,12 +7,15 @@ import { initReactI18next } from "react-i18next";
 import enCommon from "./locales/en/common.json";
 import enEntry from "./locales/en/entry.json";
 import enLayout from "./locales/en/layout.json";
+import enPlayer from "./locales/en/player.json";
 import neCommon from "./locales/ne/common.json";
 import neEntry from "./locales/ne/entry.json";
 import neLayout from "./locales/ne/layout.json";
+import nePlayer from "./locales/ne/player.json";
 import zhCommon from "./locales/zh/common.json";
 import zhEntry from "./locales/zh/entry.json";
 import zhLayout from "./locales/zh/layout.json";
+import zhPlayer from "./locales/zh/player.json";
 
 /** 对齐后端与产品：尼泊尔语 / 英语 / 中文（简体） */
 export const SUPPORTED_LANGUAGES = [
@@ -23,23 +28,26 @@ export type AppLanguage = (typeof SUPPORTED_LANGUAGES)[number]["code"];
 
 export const DEFAULT_LANGUAGE: AppLanguage = "en";
 
-const namespaces = ["common", "entry", "layout"] as const;
+const namespaces = ["common", "entry", "layout", "player"] as const;
 
 const resources = {
   en: {
     common: enCommon,
     entry: enEntry,
     layout: enLayout,
+    player: enPlayer,
   },
   ne: {
     common: neCommon,
     entry: neEntry,
     layout: neLayout,
+    player: nePlayer,
   },
   zh: {
     common: zhCommon,
     entry: zhEntry,
     layout: zhLayout,
+    player: zhPlayer,
   },
 } satisfies Record<
   AppLanguage,
@@ -53,6 +61,12 @@ export function normalizeLanguage(lang: string | undefined): AppLanguage {
   return "en";
 }
 
+export function syncDocumentLanguage(lang: AppLanguage): void {
+  if (typeof document === "undefined") return;
+
+  document.documentElement.lang = lang;
+}
+
 if (!i18n.isInitialized) {
   void i18n
     .use(LanguageDetector)
@@ -80,6 +94,12 @@ if (!i18n.isInitialized) {
         useSuspense: false,
       },
     });
+
+  syncDocumentLanguage(normalizeLanguage(i18n.resolvedLanguage ?? i18n.language));
+
+  i18n.on("languageChanged", (lang) => {
+    syncDocumentLanguage(normalizeLanguage(lang));
+  });
 }
 
 export default i18n;