feat(server): 添加游戏服务器框架 | add game server framework (#366)

**@esengine/server** - 游戏服务器框架 | Game server framework
- 文件路由系统 | File-based routing
- Room 生命周期 (onCreate, onJoin, onLeave, onTick, onDispose)
- @onMessage 装饰器 | Message handler decorator
- 玩家管理与断线处理 | Player management with auto-disconnect
- 内置 JoinRoom/LeaveRoom API | Built-in room APIs
- defineApi/defineMsg 类型安全辅助函数 | Type-safe helpers

**create-esengine-server** - CLI 脚手架工具 | CLI scaffolding
- 生成 shared/server/client 项目结构 | Project structure
- 类型安全的协议定义 | Type-safe protocol definitions
- 包含 GameRoom 示例 | Example implementation

**其他 | Other**
- 删除旧的 network-server 包 | Remove old network-server
- 更新服务器文档 | Update server documentation

packages/framework/server/src/index.ts

@@ -0,0 +1,52 @@
+/**
+ * @zh ESEngine 游戏服务器框架
+ * @en ESEngine Game Server Framework
+ *
+ * @example
+ * ```typescript
+ * import { createServer, Room, onMessage } from '@esengine/server'
+ *
+ * class GameRoom extends Room {
+ *     maxPlayers = 4
+ *     tickRate = 20
+ *
+ *     onJoin(player) {
+ *         this.broadcast('Joined', { id: player.id })
+ *     }
+ *
+ *     @onMessage('Move')
+ *     handleMove(data, player) {
+ *         // handle move
+ *     }
+ * }
+ *
+ * const server = await createServer({ port: 3000 })
+ * server.define('game', GameRoom)
+ * await server.start()
+ * ```
+ */
+
+// Core
+export { createServer } from './core/server.js'
+
+// Helpers
+export { defineApi, defineMsg } from './helpers/define.js'
+
+// Room System
+export { Room, type RoomOptions } from './room/Room.js'
+export { Player, type IPlayer } from './room/Player.js'
+export { onMessage } from './room/decorators.js'
+
+// Types
+export type {
+    ServerConfig,
+    ServerConnection,
+    GameServer,
+    ApiContext,
+    MsgContext,
+    ApiDefinition,
+    MsgDefinition,
+} from './types/index.js'
+
+// Re-export useful types from @esengine/rpc
+export { RpcError, ErrorCode } from '@esengine/rpc'