feat(antigravity): 令牌刷新失败及创建账号时也设置隐私

- token_refresh: 不可重试错误和重试耗尽两条路径添加 ensureAntigravityPrivacy
- admin_service: CreateAccount 为 Antigravity OAuth 账号异步设置隐私

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

backend/internal/service/admin_service.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"net/http"
 	"strings"
 	"time"
@@ -1587,6 +1588,18 @@ func (s *adminServiceImpl) CreateAccount(ctx context.Context, input *CreateAccou
 		}
 	}
 
+	// Antigravity OAuth 账号：创建后异步设置隐私
+	if account.Platform == PlatformAntigravity && account.Type == AccountTypeOAuth {
+		go func() {
+			defer func() {
+				if r := recover(); r != nil {
+					slog.Error("create_account_antigravity_privacy_panic", "account_id", account.ID, "recover", r)
+				}
+			}()
+			s.EnsureAntigravityPrivacy(context.Background(), account)
+		}()
+	}
+
 	return account, nil
 }