fix(auth): 修复注册接口中的邀请码参数处理

- 将 RegisterRequestDto 和 RegisterPayload 中的 invite_code 字段改为可选字段
- 修改 registerWithPassword 函数中的请求体构建逻辑，仅在有值时包含邀请码参数
- 移除邀请码验证 schema 中的必填校验规则
- 更新云开发预览配置文件中的端口和进程 ID 信息

.cloudbase-sites/preview.json

@@ -1,12 +1,12 @@
 {
-  "pid": 98343,
-  "port": 17174,
+  "pid": 24641,
+  "port": 17175,
   "host": "0.0.0.0",
   "base": "/",
   "framework": "vite-react",
-  "command": "/Users/jiaunun/.nvm/versions/node/v24.15.0/bin/node /Users/jiaunun/Desktop/36-character-flower/node_modules/vite/bin/vite.js --host 0.0.0.0 --port 17174 --strictPort --base /",
-  "internalUrl": "http://127.0.0.1:17174/",
-  "logPath": "/Users/jiaunun/Desktop/36-character-flower/.cloudbase-sites/logs/preview-1784093877629.log",
+  "command": "/Users/jiaunun/.nvm/versions/node/v24.15.0/bin/node /Users/jiaunun/Desktop/36-character-flower/node_modules/vite/bin/vite.js --host 0.0.0.0 --port 17175 --strictPort --base /",
+  "internalUrl": "http://127.0.0.1:17175/",
+  "logPath": "/Users/jiaunun/Desktop/36-character-flower/.cloudbase-sites/logs/preview-1784622161040.log",
   "cwd": "/Users/jiaunun/Desktop/36-character-flower",
-  "startedAt": "2026-07-15T05:37:58.655Z"
+  "startedAt": "2026-07-21T08:22:42.070Z"
 }