resolving-icon-font-inheritance

# WPF CustomControl Icon Font Inheritance Issue Resolution

## Problem Scenario

When using Segoe Fluent Icons font in WPF CustomControl, **TextBlocks within the same ControlTemplate inherit the icon font, causing text to render incorrectly**.

### Symptoms
- Button text displays as square boxes (□) or strange symbols
- Icons display correctly but regular text doesn't render

### Cause
WPF's `FontFamily` is inherited to child elements following the Visual Tree. When `FontFamily="Segoe Fluent Icons"` is set on a TextBlock for icons within a ControlTemplate, other TextBlocks in the same container may inherit this font.

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## Solution

### Explicitly Specify FontFamily on Text-Displaying Elements

```xml
<!-- IconButton ControlTemplate Example -->
<ControlTemplate TargetType="{x:Type local:IconButton}">
    <Border Background="{TemplateBinding Background}"
            BorderBrush="{TemplateBinding BorderBrush}"
            BorderThickness="{TemplateBinding BorderThickness}">
        <StackPanel Orientation="{TemplateBinding Orientation}"
                    HorizontalAlignment="Center"
                    VerticalAlignment="Center">

            <!-- Icon: Use Segoe Fluent Icons -->
            <TextBlock x:Name="PART_Icon"
                       Text="{TemplateBinding Icon}"
                       FontFamily="Segoe Fluent Icons, Segoe MDL2 Assets"
                       FontSize="{TemplateBinding IconSize}"
                       Foreground="{TemplateBinding Foreground}" />

            <!-- Text: Explicitly specify Segoe UI (Important!) -->
            <TextBlock x:Name="PART_Text"
                       Text="{TemplateBinding Text}"
                       FontFamily="Segoe UI"
                       FontSize="12"
                       Foreground="{TemplateBinding Foreground}"
                       VerticalAlignment="Center" />
        </StackPanel>
    </Border>
</ControlTemplate>
```

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## Key Points

1. **Apply icon font only to specific element**: Specify