fix: convert metricDate string to Date for trend chart rendering

campus_health_app/frontend/campus-health-app/src/app/modules/monitoring/monitoring.component.ts

@@ -255,14 +255,14 @@ export class MonitoringComponent implements OnInit, OnDestroy {
           this.heartRateHistory = rows
             .filter((r: any) => r.restingHeartRate != null)
             .map((r: any) => ({
-              date: r.metricDate,
+              date: new Date(r.metricDate),
               value: Number(r.restingHeartRate),
               status: 'normal' as const
             }));
           this.bloodOxygenHistory = rows
             .filter((r: any) => r.avgOxygenSaturation != null)
             .map((r: any) => ({
-              date: r.metricDate,
+              date: new Date(r.metricDate),
               value: Number(r.avgOxygenSaturation),
               status: 'normal' as const
             }));