feat: 全站多语言支持 (i18n)，lang=en 显示英文，其余默认中文

新增 src/lib/locale.ts 作为统一多语言入口，覆盖前台支付链路、
管理后台、API/服务层错误文案，共 35 个文件。URL 参数 lang 全链路透传，
包括 Stripe return_url、页面跳转、layout html lang 属性等。

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

src/app/api/admin/orders/[id]/cancel/route.ts

@@ -1,19 +1,26 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { verifyAdminToken, unauthorizedResponse } from '@/lib/admin-auth';
+import { resolveLocale } from '@/lib/locale';
 import { adminCancelOrder } from '@/lib/order/service';
 import { handleApiError } from '@/lib/utils/api';
 
 export async function POST(request: NextRequest, { params }: { params: Promise<{ id: string }> }) {
-  if (!(await verifyAdminToken(request))) return unauthorizedResponse();
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
+
+  const locale = resolveLocale(request.nextUrl.searchParams.get('lang'));
 
   try {
     const { id } = await params;
-    const outcome = await adminCancelOrder(id);
+    const outcome = await adminCancelOrder(id, locale);
     if (outcome === 'already_paid') {
-      return NextResponse.json({ success: true, status: 'PAID', message: '订单已支付完成' });
+      return NextResponse.json({
+        success: true,
+        status: 'PAID',
+        message: locale === 'en' ? 'Order has already been paid' : '订单已支付完成',
+      });
     }
     return NextResponse.json({ success: true });
   } catch (error) {
-    return handleApiError(error, '取消订单失败');
+    return handleApiError(error, locale === 'en' ? 'Cancel order failed' : '取消订单失败', request);
   }
 }

src/app/api/admin/orders/[id]/retry/route.ts

@@ -1,16 +1,19 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { verifyAdminToken, unauthorizedResponse } from '@/lib/admin-auth';
+import { resolveLocale } from '@/lib/locale';
 import { retryRecharge } from '@/lib/order/service';
 import { handleApiError } from '@/lib/utils/api';
 
 export async function POST(request: NextRequest, { params }: { params: Promise<{ id: string }> }) {
-  if (!(await verifyAdminToken(request))) return unauthorizedResponse();
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
+
+  const locale = resolveLocale(request.nextUrl.searchParams.get('lang'));
 
   try {
     const { id } = await params;
-    await retryRecharge(id);
+    await retryRecharge(id, locale);
     return NextResponse.json({ success: true });
   } catch (error) {
-    return handleApiError(error, '重试充值失败');
+    return handleApiError(error, locale === 'en' ? 'Recharge retry failed' : '重试充值失败', request);
   }
 }

src/app/api/admin/orders/[id]/route.ts

@@ -1,11 +1,13 @@
 import { NextRequest, NextResponse } from 'next/server';
 import { prisma } from '@/lib/db';
 import { verifyAdminToken, unauthorizedResponse } from '@/lib/admin-auth';
+import { resolveLocale } from '@/lib/locale';
 
 export async function GET(request: NextRequest, { params }: { params: Promise<{ id: string }> }) {
-  if (!(await verifyAdminToken(request))) return unauthorizedResponse();
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
 
   const { id } = await params;
+  const locale = resolveLocale(request.nextUrl.searchParams.get('lang'));
 
   const order = await prisma.order.findUnique({
     where: { id },
@@ -17,7 +19,7 @@ export async function GET(request: NextRequest, { params }: { params: Promise<{
   });
 
   if (!order) {
-    return NextResponse.json({ error: '订单不存在' }, { status: 404 });
+    return NextResponse.json({ error: locale === 'en' ? 'Order not found' : '订单不存在' }, { status: 404 });
   }
 
   return NextResponse.json({

src/app/api/admin/refund/route.ts

@@ -3,6 +3,7 @@ import { z } from 'zod';
 import { verifyAdminToken, unauthorizedResponse } from '@/lib/admin-auth';
 import { processRefund } from '@/lib/order/service';
 import { handleApiError } from '@/lib/utils/api';
+import { resolveLocale } from '@/lib/locale';
 
 const refundSchema = z.object({
   order_id: z.string().min(1),
@@ -11,24 +12,30 @@ const refundSchema = z.object({
 });
 
 export async function POST(request: NextRequest) {
-  if (!(await verifyAdminToken(request))) return unauthorizedResponse();
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
+
+  const locale = resolveLocale(request.nextUrl.searchParams.get('lang'));
 
   try {
     const body = await request.json();
     const parsed = refundSchema.safeParse(body);
 
     if (!parsed.success) {
-      return NextResponse.json({ error: '参数错误', details: parsed.error.flatten().fieldErrors }, { status: 400 });
+      return NextResponse.json(
+        { error: locale === 'en' ? 'Invalid parameters' : '参数错误', details: parsed.error.flatten().fieldErrors },
+        { status: 400 },
+      );
     }
 
     const result = await processRefund({
       orderId: parsed.data.order_id,
       reason: parsed.data.reason,
       force: parsed.data.force,
+      locale,
     });
 
     return NextResponse.json(result);
   } catch (error) {
-    return handleApiError(error, '退款失败');
+    return handleApiError(error, locale === 'en' ? 'Refund failed' : '退款失败', request);
   }
 }

src/app/api/user/route.ts

@@ -3,17 +3,19 @@ import { getUser, getCurrentUserByToken } from '@/lib/sub2api/client';
 import { getEnv } from '@/lib/config';
 import { queryMethodLimits } from '@/lib/order/limits';
 import { initPaymentProviders, paymentRegistry } from '@/lib/payment';
-import { PAYMENT_TYPE_META } from '@/lib/pay-utils';
+import { getPaymentDisplayInfo } from '@/lib/pay-utils';
+import { resolveLocale } from '@/lib/locale';
 
 export async function GET(request: NextRequest) {
+  const locale = resolveLocale(request.nextUrl.searchParams.get('lang'));
   const userId = Number(request.nextUrl.searchParams.get('user_id'));
   if (!userId || isNaN(userId) || userId <= 0) {
-    return NextResponse.json({ error: '无效的用户 ID' }, { status: 400 });
+    return NextResponse.json({ error: locale === 'en' ? 'Invalid user ID' : '无效的用户 ID' }, { status: 400 });
   }
 
   const token = request.nextUrl.searchParams.get('token')?.trim();
   if (!token) {
-    return NextResponse.json({ error: '缺少 token 参数' }, { status: 401 });
+    return NextResponse.json({ error: locale === 'en' ? 'Missing token parameter' : '缺少 token 参数' }, { status: 401 });
   }
 
   try {
@@ -22,11 +24,11 @@ export async function GET(request: NextRequest) {
     try {
       tokenUser = await getCurrentUserByToken(token);
     } catch {
-      return NextResponse.json({ error: '无效的 token' }, { status: 401 });
+      return NextResponse.json({ error: locale === 'en' ? 'Invalid token' : '无效的 token' }, { status: 401 });
     }
 
     if (tokenUser.id !== userId) {
-      return NextResponse.json({ error: '无权访问该用户信息' }, { status: 403 });
+      return NextResponse.json({ error: locale === 'en' ? 'Forbidden to access this user' : '无权访问该用户信息' }, { status: 403 });
     }
 
     const env = getEnv();
@@ -40,17 +42,16 @@ export async function GET(request: NextRequest) {
     // 1. 检测同 label 冲突：多个启用渠道有相同的显示名，自动标记默认 sublabel（provider 名）
     const labelCount = new Map<string, string[]>();
     for (const type of enabledTypes) {
-      const meta = PAYMENT_TYPE_META[type];
-      if (!meta) continue;
-      const types = labelCount.get(meta.label) || [];
+      const { channel } = getPaymentDisplayInfo(type, locale);
+      const types = labelCount.get(channel) || [];
       types.push(type);
-      labelCount.set(meta.label, types);
+      labelCount.set(channel, types);
     }
     for (const [, types] of labelCount) {
       if (types.length > 1) {
         for (const type of types) {
-          const meta = PAYMENT_TYPE_META[type];
-          if (meta) sublabelOverrides[type] = meta.provider;
+          const { provider } = getPaymentDisplayInfo(type, locale);
+          if (provider) sublabelOverrides[type] = provider;
         }
       }
     }
@@ -85,9 +86,9 @@ export async function GET(request: NextRequest) {
   } catch (error) {
     const message = error instanceof Error ? error.message : String(error);
     if (message === 'USER_NOT_FOUND') {
-      return NextResponse.json({ error: '用户不存在' }, { status: 404 });
+      return NextResponse.json({ error: locale === 'en' ? 'User not found' : '用户不存在' }, { status: 404 });
     }
     console.error('Get user error:', error);
-    return NextResponse.json({ error: '获取用户信息失败' }, { status: 500 });
+    return NextResponse.json({ error: locale === 'en' ? 'Failed to fetch user info' : '获取用户信息失败' }, { status: 500 });
   }
 }