feat: add Avalonia Zafiro development, layout, and viewmodel skills

skills/avalonia-layout-zafiro/behaviors.md

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+# Interactions and Logic
+
+To keep XAML clean and maintainable, minimize logic in views and avoid excessive use of converters.
+
+## 🎭 Xaml.Interaction.Behaviors
+
+Use `Interaction.Behaviors` to handle UI-related logic that doesn't belong in the ViewModel, such as focus management, animations, or specialized event handling.
+
+```xml
+<TextBox Text="{Binding Address}">
+    <Interaction.Behaviors>
+        <UntouchedClassBehavior />
+    </Interaction.Behaviors>
+</TextBox>
+```
+
+### Why use Behaviors?
+- **Encapsulation**: UI logic is contained in a reusable behavior class.
+- **Clean XAML**: Avoids code-behind and complex XAML triggers.
+- **Testability**: Behaviors can be tested independently of the View.
+
+## 🚫 Avoiding Converters
+
+Converters often lead to "magical" logic hidden in XAML. Whenever possible, prefer:
+
+1.  **ViewModel Properties**: Let the ViewModel provide the final data format (e.g., a `string` formatted for display).
+2.  **MultiBinding**: Use for simple logic combinations (And/Or) directly in XAML.
+3.  **Behaviors**: For more complex interactions that involve state or events.
+
+### When to use Converters?
+Only use them when the conversion is purely visual and highly reusable across different contexts (e.g., `BoolToOpacityConverter`).
+
+## 🧩 Simplified Interactions
+
+If you find yourself needing a complex converter or behavior, consider if the component can be simplified or if the data model can be adjusted to make the view binding more direct.