fix: staged hours no longer leak closed values to days before effective date

The else-if chain in GetWorkingHours/computeAvailableHours entered the staged change block for ALL days when a pending change existed, but only applied hours for future dates — leaving earlier days as zero-value (closed). Moved the effective date check into the else-if condition so early days fall through to default hours.

backend/handlers/scheduling/default-hours.go

@@ -382,17 +382,14 @@ func GetWorkingHours(w http.ResponseWriter, r *http.Request) {
 			day.EndTime = applied.EndTime
 			day.IsOpen = applied.IsOpen
 			day.Source = "exceptional"
-		} else if stagedChange != nil {
-			dayDateStr := d.Format("2006-01-02")
-			if dayDateStr >= stagedChange.EffectiveDate {
-				for _, sh := range stagedChange.Hours {
-					if sh.Weekday == weekday {
-						day.StartTime = sh.StartTime
-						day.EndTime = sh.EndTime
-						day.IsOpen = sh.IsOpen
-						day.Source = "default"
-						break
-					}
+		} else if stagedChange != nil && d.Format("2006-01-02") >= stagedChange.EffectiveDate {
+			for _, sh := range stagedChange.Hours {
+				if sh.Weekday == weekday {
+					day.StartTime = sh.StartTime
+					day.EndTime = sh.EndTime
+					day.IsOpen = sh.IsOpen
+					day.Source = "default"
+					break
 				}
 			}
 		} else if def, ok := defaultMap[weekday]; ok {