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>

package.json

@@ -0,0 +1,32 @@
+{
+  "name": "sso-mock",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev -p 5501",
+    "build": "next build",
+    "start": "next start"
+  },
+  "dependencies": {
+    "@mantine/core": "^8.3.6",
+    "@mantine/form": "^8.3.6",
+    "@mantine/hooks": "^8.3.6",
+    "@mantine/notifications": "8.3.18",
+    "@tabler/icons-react": "^3.35.0",
+    "clsx": "^2.1.1",
+    "crypto-js": "^4.2.0",
+    "next": "16.0.1",
+    "react": "19.2.0",
+    "react-dom": "19.2.0",
+    "zustand": "^5.0.8"
+  },
+  "devDependencies": {
+    "@types/crypto-js": "^4.2.2",
+    "@types/node": "^20",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "postcss-preset-mantine": "^1.18.0",
+    "postcss-simple-vars": "^7.0.1",
+    "typescript": "^5"
+  }
+}