Write the disabled accent glow as 'none', which this Avalonia can parse

src/DodoSSH.Client.App/App.axaml

@@ -233,14 +233,20 @@
       BoxShadow is cleared here too, and that is new alongside the gradient: the base rule now sets a glow
       that reads as "this is lit and wants pressing", which is the opposite of what a disabled control
       should say. Left unset it would still apply — the base rule's Setter is still in effect wherever a
-      more specific one does not override it — so the glow has to be named here, as the empty string
+      more specific one does not override it — so the glow has to be named here, as "none", to go away.
-      BoxShadows parses to "no shadows", to go away.
+
+      ◆ "none" RATHER THAN THE EMPTY STRING. The remark this replaced claimed an empty string parses to "no
+      shadows", and it does not on the Avalonia this project builds against — BoxShadowsTypeConverter throws
+      an InvalidCastException on it instead, which failed silently at style-sheet load time in nothing that
+      exercises this rule's own screen and loudly in every headless layout test that lays out any window at
+      all, because Application.Styles is global. "none" is the literal this converter does accept for an
+      empty BoxShadows.
     -->
     <Style Selector="Button.accent:disabled /template/ ContentPresenter#PART_ContentPresenter">
       <Setter Property="Background" Value="Transparent" />
       <Setter Property="BorderBrush" Value="{StaticResource BorderFaint}" />
       <Setter Property="BorderThickness" Value="1" />
-      <Setter Property="BoxShadow" Value="" />
+      <Setter Property="BoxShadow" Value="none" />
       <Setter Property="Foreground" Value="{StaticResource TextFaint}" />
     </Style>