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

skills/avalonia-zafiro-development/zafiro-shortcuts.md

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+# Zafiro Reactive Shortcuts
+
+Use these Zafiro extension methods to replace standard, more verbose Reactive and DynamicData patterns.
+
+## General Observable Helpers
+
+| Standard Pattern | Zafiro Shortcut |
+| :--- | :--- |
+| `Replay(1).RefCount()` | `ReplayLastActive()` |
+| `Select(_ => Unit.Default)` | `ToSignal()` |
+| `Select(b => !b)` | `Not()` |
+| `Where(b => b).ToSignal()` | `Trues()` |
+| `Where(b => !b).ToSignal()` | `Falses()` |
+| `Select(x => x is null)` | `Null()` |
+| `Select(x => x is not null)` | `NotNull()` |
+| `Select(string.IsNullOrWhiteSpace)` | `NullOrWhitespace()` |
+| `Select(s => !string.IsNullOrWhiteSpace(s))` | `NotNullOrEmpty()` |
+
+## Result & Maybe Extensions
+
+| Standard Pattern | Zafiro Shortcut |
+| :--- | :--- |
+| `Where(r => r.IsSuccess).Select(r => r.Value)` | `Successes()` |
+| `Where(r => r.IsFailure).Select(r => r.Error)` | `Failures()` |
+| `Where(m => m.HasValue).Select(m => m.Value)` | `Values()` |
+| `Where(m => !m.HasValue).ToSignal()` | `Empties()` |
+
+## Lifecycle Management
+
+| Description | Method |
+| :--- | :--- |
+| Dispose previous item before emitting new one | `DisposePrevious()` |
+| Manage lifecycle within a disposable | `DisposeWith(disposables)` |
+
+## Command & Interaction
+
+| Description | Method |
+| :--- | :--- |
+| Add metadata/text to a ReactiveCommand | `Enhance(text, name)` |
+| Automatically show errors in UI | `HandleErrorsWith(notificationService)` |
+
+> [!TIP]
+> Always check `Zafiro.Reactive.ObservableMixin` and `Zafiro.CSharpFunctionalExtensions.ObservableExtensions` before writing custom Rx logic.