style: use the FontAwesome circle-question glyph for docs buttons

Its counter stays legible at 16px where the FluentIcons filled variant closes
up, and it matches the FontAwesome help glyphs already used elsewhere in the app.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: mohnjiles

StabilityMatrix.Avalonia/Styles/ControlThemes/DocsHelpButtonStyles.axaml

@@ -2,7 +2,7 @@
     xmlns="https://github.com/avaloniaui"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:controls="clr-namespace:StabilityMatrix.Avalonia.Controls"
-    xmlns:fluentIcons="clr-namespace:FluentIcons.Avalonia.Fluent;assembly=FluentIcons.Avalonia.Fluent"
+    xmlns:icons="https://github.com/projektanker/icons.avalonia"
     xmlns:lang="clr-namespace:StabilityMatrix.Avalonia.Languages">
 
     <Design.PreviewWith>
@@ -33,14 +33,11 @@
                     Padding="{TemplateBinding Padding}"
                     Background="{TemplateBinding Background}"
                     CornerRadius="{TemplateBinding CornerRadius}">
-                    <!--  FluentIcons SymbolIcon measures greedily without explicit Width/Height  -->
-                    <fluentIcons:SymbolIcon
-                        Width="16"
-                        Height="16"
+                    <!--  Matches the FontAwesome help glyphs used elsewhere in the app  -->
+                    <icons:Icon
                         FontSize="16"
                         Foreground="{TemplateBinding Foreground}"
-                        IconVariant="Filled"
-                        Symbol="QuestionCircle" />
+                        Value="fa-solid fa-circle-question" />
                 </Border>
             </ControlTemplate>
         </Setter>

StabilityMatrix.UITests/DocsHelpButtonTests.cs

@@ -1,6 +1,6 @@
 using Avalonia.Controls;
 using Avalonia.VisualTree;
-using FluentIcons.Avalonia.Fluent;
+using Projektanker.Icons.Avalonia;
 using StabilityMatrix.Avalonia.Controls;
 using StabilityMatrix.Core.Models.Documentation;
 
@@ -21,9 +21,10 @@ public void DocsHelpButton_ShouldResolveControlTheme()
 
         window.Show();
 
-        var icon = button.GetVisualDescendants().OfType<SymbolIcon>().FirstOrDefault();
+        var icon = button.GetVisualDescendants().OfType<Icon>().FirstOrDefault();
 
         Assert.NotNull(icon);
+        Assert.Equal("fa-solid fa-circle-question", icon.Value);
         Assert.Equal("Hand", button.Cursor?.ToString());
     }
 }