chore: initial commit of sso-mock SSO login service

Next.js + Mantine mock SSO service providing account/password, phone
verify-code, and Feishu QR login. Issues a one-time sso_code that the
external app exchanges for user info.

Includes:
- Feishu callback fix: guard against duplicate/concurrent /api/login
  submissions of the same single-use authorization code (feishuLogin
  once-guard + memoized onLoginSuccess to stop effect re-fire).
- ADAPTATION_GUIDE.md: how to switch from the in-memory code store to
  the real backend auth/index + inner_get_user_info endpoints.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/mock/users/route.ts

@@ -0,0 +1,15 @@
+import { NextResponse } from 'next/server'
+
+/**
+ * Mock 用户列表接口（用于测试）
+ * GET /api/mock/users
+ */
+export async function GET() {
+  const users = [
+    { account: 'admin', password: '123456', name: '管理员', phone: '13800138000', roles: ['admin'] },
+    { account: 'user01', password: '123456', name: '测试用户', phone: '13900139000', roles: ['user'] },
+    { account: 'zhangsan', password: '123456', name: '张三', phone: '13700137000', roles: ['user', 'editor'] },
+  ]
+
+  return NextResponse.json({ users })
+}