fix: MonitoringController Timestamp 캐스팅 오류 수정

- JdbcTemplate이 timestamptz를 java.sql.Timestamp로 반환하는 케이스 처리
- toLocalDateTime() 유틸 메서드로 Timestamp/OffsetDateTime/LocalDateTime 통합 변환

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/java/gc/mda/signal_batch/monitoring/controller/MonitoringController.java

@@ -50,14 +50,8 @@ public class MonitoringController {
                 """
             );
 
-            Object aisRaw = aisLatest.get("latest_update_time");
-            LocalDateTime aisTime = null;
-            if (aisRaw instanceof java.time.OffsetDateTime odt) {
-                aisTime = odt.toLocalDateTime();
-            } else if (aisRaw instanceof LocalDateTime ldt) {
-                aisTime = ldt;
-            }
-            LocalDateTime queryTime = (LocalDateTime) queryLatest.get("latest_processed_time");
+            LocalDateTime aisTime = toLocalDateTime(aisLatest.get("latest_update_time"));
+            LocalDateTime queryTime = toLocalDateTime(queryLatest.get("latest_processed_time"));
 
             long delayMinutes = 0;
             String delayStatus = "NORMAL";
@@ -233,4 +227,15 @@ public class MonitoringController {
 
         return quality;
     }
+
+    private static LocalDateTime toLocalDateTime(Object raw) {
+        if (raw instanceof java.sql.Timestamp ts) {
+            return ts.toLocalDateTime();
+        } else if (raw instanceof java.time.OffsetDateTime odt) {
+            return odt.toLocalDateTime();
+        } else if (raw instanceof LocalDateTime ldt) {
+            return ldt;
+        }
+        return null;
+    }
 }