优化: 兑换上限视为成功

- classifyRetryStop 添加 success 返回值
- 兑换上限(2019)现在算作抢购成功，而非失败
- 前端状态显示：兑换上限显示为「已抢到」
- 设置弹窗说明更新

以日志为例：成功率从 0.6% 提升到 39.4%（63/160）

internal/seckill/scheduler.go

@@ -391,7 +391,7 @@ func (s *Scheduler) executeRound(attempts []types.ExchangeAttempt) roundOutcome
 				mu.Unlock()
 			} else {
 				logger.LogEvent("抢购", "info", "尝试: %s %s 第%d包 %s", result.Account, result.Product, result.Attempt, result.Message)
-				terminalAccount, terminalProduct, reason := classifyRetryStop(result.Message)
+				terminalAccount, terminalProduct, isSuccess, reason := classifyRetryStop(result.Message)
 				if terminalAccount || terminalProduct {
 					mu.Lock()
 					if terminalAccount {
@@ -400,6 +400,12 @@ func (s *Scheduler) executeRound(attempts []types.ExchangeAttempt) roundOutcome
 					if terminalProduct {
 						outcome.stoppedProducts[attempt.Product.CommodityID] = reason
 					}
+					// 兑换上限也算成功
+					if isSuccess {
+						outcome.successAccounts[attempt.Account.Name] = true
+						logger.LogEvent("抢购", "success", "成功（兑换上限）: %s %s 第%d包", result.Account, result.Product, result.Attempt)
+						go image.SaveSuccessImage(attempt.Account, attempt.Product, result.RoleName, s.font, s.paths.SuccessDir)
+					}
 					mu.Unlock()
 				}
 			}
@@ -430,18 +436,18 @@ func jitterDuration(base time.Duration) time.Duration {
 	return base + jitter
 }
 
-func classifyRetryStop(message string) (account bool, product bool, reason string) {
+func classifyRetryStop(message string) (account bool, product bool, success bool, reason string) {
 	switch {
 	case strings.Contains(message, "商品本次活动库存已耗完"):
-		return true, true, "商品库存已耗完"
+		return true, true, false, "商品库存已耗完"
 	case strings.Contains(message, "您已达本次活动兑换上限"):
-		return true, false, "账号已达兑换上限"
+		return true, false, true, "已抢到（兑换上限）"
 	case strings.Contains(message, "未绑定账号"):
-		return true, false, "账号未绑定角色"
+		return true, false, false, "账号未绑定角色"
 	case strings.Contains(message, "需要开通精英手册"):
-		return true, false, "账号不满足精英手册条件"
+		return true, false, false, "账号不满足精英手册条件"
 	default:
-		return false, false, ""
+		return false, false, false, ""
 	}
 }