Add MainHUD gameplay UI, net handshake updates, and server maintenance mode.

Introduce UiManager/MainHUD prefab flow, strengthen GameNet/WsClient, and add AIServer maintenance endpoint support.

Co-authored-by: Cursor <cursoragent@cursor.com>

Doc/NetProtocol.md

@@ -19,7 +19,8 @@ Base: `https://game.xworld.ren`（Caddy → 后端）
 | --- | --- | --- | --- | --- |
 | POST | `/register` | `{"username","password"}` | `{token,pid}` | `invalid_input` / `user_exists` |
 | POST | `/login` | `{"username","password"}` | `{token,pid}` | `invalid_credentials` |
-| GET | `/health` | — | `{ok,service}` | — |
+| GET | `/health` | — | `{ok,service,maintenance}` | — |
+| GET | `/maintenance` | — | `{enabled,message}` | — |
 
 ## WebSocket
 
@@ -29,8 +30,22 @@ Base: `https://game.xworld.ren`（Caddy → 后端）
 
 - 无 token / token 无效 → HTTP 401
 - 应用层：`{"op":"hello"}` → `{"op":"hello_ack","ok":true}`；`{"op":"ping"}` → `{"op":"pong"}`
+- 维护：若 `data/maintenance.json` 中 `enabled=true`，升级后立刻下发 `{"op":"maintenance","message":"..."}` 并断开
 - 协议层 Ping/Pong 由服务端应答
 
+## 维护开关
+
+文件：`AIServer/data/maintenance.json`（与 `--db` 同目录，可用 `--maintenance` 覆盖）
+
+```json
+{ "enabled": true, "message": "今晚 2:00-4:00 维护" }
+```
+
+| GET | `/maintenance` | — | `{enabled,message}` |
+| GET | `/health` | — | 增加 `maintenance` 字段 |
+
+CDN `version.json.notice` 也会在客户端启动时弹公告（不依赖游戏服）。
+
 ## 客户端
 
 - `HotUpdate.Net.AuthApi` / `GameNet` / `WsClient`