improvement: 대시보드 TopMessage에 status 필드 추가 (#193)

- TopMessageDto에 status 필드 추가 (SendStatus.Determine 적용)
- 대시보드/이력 간 동일 건의 상태 라벨 일치 보장

Closes #193

SPMS.Application/DTOs/Stats/DashboardResponseDto.cs

@@ -69,4 +69,7 @@ public class TopMessageDto
 
     [JsonPropertyName("success_count")]
     public int SuccessCount { get; set; }
+
+    [JsonPropertyName("status")]
+    public string Status { get; set; } = string.Empty;
 }

SPMS.Application/Services/StatsService.cs

@@ -457,7 +457,8 @@ public class StatsService : IStatsService
                 Title = m.Title,
                 ServiceName = m.ServiceName,
                 TotalSendCount = m.TotalSendCount,
-                SuccessCount = m.SuccessCount
+                SuccessCount = m.SuccessCount,
+                Status = SendStatus.Determine(m.TotalSendCount, m.SuccessCount)
             }).ToList()
         };
     }