refactor: 项目架构重构 - 目录标准化 + 清理冗余

- 目录重命名: backend/wdkj-server/ → server/, frontend/ai-dimension/ → client/
- 删除 20+ 冗余文件（WDKJ 旧脚本、Windows 脚本、过时文档、设计稿）
- 更新 package.json 元数据（移除 wdkj 命名）
- 完善三级 .gitignore（根 + server + client）
- 重写 README.md 和 CHANGELOG.md
- 工具脚本移至 scripts/

server/src/models/index.js

@@ -0,0 +1,25 @@
+const User = require('./User')
+const Order = require('./Order')
+const Knowledge = require('./Knowledge')
+const ShopItem = require('./ShopItem')
+const Admin = require('./Admin')
+const AdminLog = require('./AdminLog')
+const AIChatQuota = require('./AIChatQuota')
+const AIModel = require('./AIModel')
+const LoginLog = require('./LoginLog')
+const Feedback = require('./Feedback')
+const Trend = require('./Trend')
+
+module.exports = {
+  User,
+  Order,
+  Knowledge,
+  ShopItem,
+  Admin,
+  AdminLog,
+  AIChatQuota,
+  AIModel,
+  LoginLog,
+  Feedback,
+  Trend
+}