🐛 Fix stale retention slider label when value equals the slider minimum

The FormSlider summary label was only recomputed on value changes, and the
Units dependency property defaulted to Hours. When the Minimum binding was
applied, it coerced Value (0 -> minimum) and rendered the label while Units
was still at its default. If the bound value then equaled the minimum (e.g.
an audit retention of exactly 1 day, or error retention of exactly 5 days),
no further value change occurred and the label stuck at e.g. "1 Hours".

Default Units to Days (the only unit actually used) and refresh the summary
whenever Units changes, making the label independent of binding order.

The stored setting was never affected; the defect was display-only.

Author: ramonsmits

src/ServiceControl.Config/Xaml/Controls/FormSlider.cs

@@ -70,6 +70,11 @@ protected override void OnValueChanged(double oldValue, double newValue)
         {
             base.OnValueChanged(oldValue, newValue);
 
+            RefreshSummary();
+        }
+
+        void RefreshSummary()
+        {
             var period = Units == TimeSpanUnits.Days
                 ? TimeSpan.FromDays(Math.Truncate(Value))
                 : TimeSpan.FromHours(Math.Truncate(Value));
@@ -107,8 +112,12 @@ void UpdateSummary(TimeSpan period)
         public static readonly DependencyProperty HeaderProperty =
             DependencyProperty.Register("Header", typeof(string), typeof(FormSlider), new PropertyMetadata(string.Empty));
 
+        // The summary label is computed in OnValueChanged, which can fire before the Units binding is
+        // applied (e.g. when the Minimum binding coerces Value). Refresh the summary when Units changes
+        // so the label never sticks with a unit it was not meant to use.
         public static readonly DependencyProperty UnitsProperty =
-            DependencyProperty.Register("Units", typeof(TimeSpanUnits), typeof(FormSlider));
+            DependencyProperty.Register("Units", typeof(TimeSpanUnits), typeof(FormSlider),
+                new PropertyMetadata(TimeSpanUnits.Days, (d, _) => ((FormSlider)d).RefreshSummary()));
     }
 
     public enum TimeSpanUnits