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>

utils/session.ts

@@ -0,0 +1,56 @@
+import CryptoJS from 'crypto-js'
+
+const SECRET_KEY = 'mock-sso-secret-key-2024'
+const TOKEN_KEY = 'sso_token'
+const USER_KEY = 'sso_user'
+
+export const encrypt = (data: string) => {
+  try {
+    return CryptoJS.AES.encrypt(data, SECRET_KEY).toString()
+  } catch {
+    return data
+  }
+}
+
+export const decrypt = (data: string) => {
+  try {
+    const bytes = CryptoJS.AES.decrypt(data, SECRET_KEY)
+    return bytes.toString(CryptoJS.enc.Utf8)
+  } catch {
+    return data
+  }
+}
+
+export const setAuth = (token: string, user: object) => {
+  if (typeof window === 'undefined') return
+  localStorage.setItem(TOKEN_KEY, encrypt(token))
+  localStorage.setItem(USER_KEY, encrypt(JSON.stringify(user)))
+}
+
+export const getToken = (): string | null => {
+  if (typeof window === 'undefined') return null
+  const encrypted = localStorage.getItem(TOKEN_KEY)
+  if (!encrypted) return null
+  return decrypt(encrypted)
+}
+
+export const getUser = (): object | null => {
+  if (typeof window === 'undefined') return null
+  const encrypted = localStorage.getItem(USER_KEY)
+  if (!encrypted) return null
+  try {
+    return JSON.parse(decrypt(encrypted))
+  } catch {
+    return null
+  }
+}
+
+export const clearAuth = () => {
+  if (typeof window === 'undefined') return
+  localStorage.removeItem(TOKEN_KEY)
+  localStorage.removeItem(USER_KEY)
+}
+
+export const isAuthenticated = (): boolean => {
+  return !!getToken()
+}