Refactor @objectql/server as thin wrapper to @objectql/plugin-server

完全移除现有的 server 实现逻辑，按照新的插件方式重构。

- 删除 @objectql/server 中的所有实现文件
- 将 @objectql/server 改为仅从 @objectql/plugin-server 重新导出的兼容层
- 将所有测试移至 @objectql/plugin-server 包
- 更新示例使用新的 @objectql/plugin-server 包
- 所有 129 个测试仍然通过

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

examples/integrations/express-server/package.json

@@ -27,7 +27,7 @@
   },
   "dependencies": {
     "@objectql/core": "workspace:*",
-    "@objectql/server": "workspace:*",
+    "@objectql/plugin-server": "workspace:*",
     "@objectql/types": "workspace:*",
     "@objectql/driver-sql": "workspace:*",
     "@objectql/platform-node": "workspace:*",

examples/integrations/express-server/src/index.ts

@@ -10,7 +10,7 @@ import express from 'express';
 import { ObjectQL } from '@objectql/core';
 import { SqlDriver } from '@objectql/driver-sql';
 import { ObjectLoader } from '@objectql/platform-node';
-import { createNodeHandler, createMetadataHandler, createRESTHandler } from '@objectql/server';
+import { createNodeHandler, createMetadataHandler, createRESTHandler } from '@objectql/plugin-server';
 import * as path from 'path';
 
 async function main() {