use 0 instead of start of aggregation window for creationtime in xlsx

internal/tasks/monthlyAggregate.go

@@ -265,6 +265,7 @@ func mergeMonthlyAgg(dst, src *monthlyAggVal) {
 	if src.creation > 0 && (dst.creation == 0 || src.creation < dst.creation) {
 		dst.creation = src.creation
 	}
+	// If creation is unknown in all daily summaries, leave it zero for reports (VM trace handles approximation separately).
 	if src.deletion > 0 && (dst.deletion == 0 || src.deletion < dst.deletion) {
 		dst.deletion = src.deletion
 	}