feat(openai): Mobile RT 补全 plan_type、精确匹配账号、刷新时自动设置隐私

1. accounts/check 补全 plan_type：当 id_token 缺少 plan_type（如 Mobile RT），
   自动调用 accounts/check 端点获取订阅类型
2. orgID 精确匹配账号：从 JWT 提取 poid 匹配正确账号，避免 Go map
   遍历顺序随机导致 plan_type 不稳定
3. RT 刷新时设置隐私：调用 disableOpenAITraining 关闭训练数据共享，
   结果存入 extra.privacy_mode，后续跳过重复设置

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/composables/useOpenAIOAuth.ts

@@ -14,6 +14,7 @@ export interface OpenAITokenInfo {
   email?: string
   name?: string
   plan_type?: string
+  privacy_mode?: string
   // OpenAI specific IDs (extracted from ID Token)
   chatgpt_account_id?: string
   chatgpt_user_id?: string
@@ -231,6 +232,9 @@ export function useOpenAIOAuth(options?: UseOpenAIOAuthOptions) {
     if (tokenInfo.name) {
       extra.name = tokenInfo.name
     }
+    if (tokenInfo.privacy_mode) {
+      extra.privacy_mode = tokenInfo.privacy_mode
+    }
     return Object.keys(extra).length > 0 ? extra : undefined
   }