fix(ai): 文档助手按页面语言读正文，/en 页不再拿到中文原文

chat 路由 source.getPage(slugArray) 没传 locale，fumadocs 固定返回 zh 原文，
英文文档页的助手上下文一直是中文。DocsAssistant 的 pageContext 带上 locale，
路由用 hasLocale 校验后传给 getPage；非法值走 fallback（zh）。

Author: github-actions[bot]

app/[locale]/docs/[...slug]/page.tsx

@@ -214,6 +214,7 @@ export default async function DocPage({ params }: Param) {
           title: page.data.title,
           description: page.data.description,
           slug: slug?.join("/"),
+          locale,
         }}
       />
     </>

app/api/chat/route.ts

@@ -2,6 +2,8 @@ import { streamText, UIMessage, convertToModelMessages } from "ai";
 import { getModel, requiresApiKey, type AIProvider } from "@/lib/ai/models";
 import { buildSystemMessage } from "@/lib/ai/prompt";
 import { source } from "@/lib/source";
+import { routing } from "@/i18n/routing";
+import { hasLocale } from "next-intl";
 import { limitChat, rateLimitResponse } from "@/lib/rate-limit";
 import fs from "fs/promises";
 import path from "path";
@@ -20,6 +22,7 @@ interface ChatRequest {
     description?: string;
     content?: string;
     slug?: string;
+    locale?: string;
   };
   provider?: AIProvider;
   apiKey?: string;
@@ -140,7 +143,11 @@ export async function POST(req: Request) {
     if (pageContext?.slug && !pageContext.content) {
       try {
         const slugArray = pageContext.slug.split("/");
-        const page = source.getPage(slugArray);
+        // 不传 locale 会固定拿到 zh 原文，/en 页的助手就读中文；非法值交给 fallback（zh）
+        const locale = hasLocale(routing.locales, pageContext.locale)
+          ? pageContext.locale
+          : undefined;
+        const page = source.getPage(slugArray, locale);
 
         if (page) {
           const cachedContent = mdxContentCache.get(page.path);

app/components/DocsAssistant.tsx

@@ -19,6 +19,7 @@ interface PageContext {
   title?: string;
   description?: string;
   slug?: string;
+  locale?: string;
 }
 
 export interface WelcomeSuggestion {