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

skills/avalonia-zafiro-development/SKILL.md

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+---
+name: avalonia-zafiro-development
+description: Mandatory skills, conventions, and behavioral rules for Avalonia UI development using the Zafiro toolkit.
+---
+
+# Avalonia Zafiro Development
+
+This skill defines the mandatory conventions and behavioral rules for developing cross-platform applications with Avalonia UI and the Zafiro toolkit. These rules prioritize maintainability, correctness, and a functional-reactive approach.
+
+## Core Pillars
+
+1.  **Functional-Reactive MVVM**: Pure MVVM logic using DynamicData and ReactiveUI.
+2.  **Safety & Predictability**: Explicit error handling with `Result` types and avoidance of exceptions for flow control.
+3.  **Cross-Platform Excellence**: Strictly Avalonia-independent ViewModels and composition-over-inheritance.
+4.  **Zafiro First**: Leverage existing Zafiro abstractions and helpers to avoid redundancy.
+
+## Guides
+
+- [Core Technical Skills & Architecture](core-technical-skills.md): Fundamental skills and architectural principles.
+- [Naming & Coding Standards](naming-standards.md): Rules for naming, fields, and error handling.
+- [Avalonia, Zafiro & Reactive Rules](avalonia-reactive-rules.md): Specific guidelines for UI, Zafiro integration, and DynamicData pipelines.
+- [Zafiro Shortcuts](zafiro-shortcuts.md): Concise mappings for common Rx/Zafiro operations.
+- [Common Patterns](patterns.md): Advanced patterns like `RefreshableCollection` and Validation.
+
+## Procedure Before Writing Code
+
+1.  **Search First**: Search the codebase for similar implementations or existing Zafiro helpers.
+2.  **Reusable Extensions**: If a helper is missing, propose a new reusable extension method instead of inlining complex logic.
+3.  **Reactive Pipelines**: Ensure DynamicData operators are used instead of plain Rx where applicable.

skills/avalonia-zafiro-development/avalonia-reactive-rules.md

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+# Avalonia, Zafiro & Reactive Rules
+
+## Avalonia UI Rules
+
+- **Strict Avalonia**: Never use `System.Drawing`; always use Avalonia types.
+- **Pure ViewModels**: ViewModels must **never** reference Avalonia types.
+- **Bindings Over Code-Behind**: Logic should be driven by bindings.
+- **DataTemplates**: Prefer explicit `DataTemplate`s and typed `DataContext`s.
+- **VisualStates**: Avoid using `VisualStates` unless absolutely required.
+
+## Zafiro Guidelines
+
+- **Prefer Abstractions**: Always look for existing Zafiro helpers, extension methods, and abstractions before re-implementing logic.
+- **Validation**: Use Zafiro's `ValidationRule` and validation extensions instead of ad-hoc reactive logic.
+
+## DynamicData & Reactive Rules
+
+### The Mandatory Approach
+
+- **Operator Preference**: Always prefer **DynamicData** operators (`Connect`, `Filter`, `Transform`, `Sort`, `Bind`, `DisposeMany`) over plain Rx operators when working with collections.
+- **Readable Pipelines**: Build and maintain pipelines as a single, readable chain.
+- **Lifecycle**: Use `DisposeWith` for lifecycle management.
+- **Minimal Subscriptions**: Subscriptions should be minimal, centralized, and strictly for side-effects.
+
+### Forbidden Anti-Patterns
+
+- **Ad-hoc Sources**: Do NOT create new `SourceList` / `SourceCache` on the fly for local problems.
+- **Logic in Subscribe**: Do NOT place business logic inside `Subscribe`.
+- **Operator Mismatch**: Do NOT use `System.Reactive` operators if a DynamicData equivalent exists.
+
+### Canonical Patterns
+
+**Validation of Dynamic Collections:**
+```csharp
+this.ValidationRule(
+        StagesSource
+            .Connect()
+            .FilterOnObservable(stage => stage.IsValid)
+            .IsEmpty(),
+        b => !b,
+        _ => "Stages are not valid")
+    .DisposeWith(Disposables);
+```
+
+**Filtering Nulls:**
+Use `WhereNotNull()` in reactive pipelines.
+```csharp
+this.WhenAnyValue(x => x.DurationPreset).WhereNotNull()
+```

skills/avalonia-zafiro-development/core-technical-skills.md

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+# Core Technical Skills & Architecture
+
+## Mandatory Expertise
+
+The developer must possess strong expertise in:
+- **C# and modern .NET**: Utilizing the latest features of the language and framework.
+- **Avalonia UI**: For cross-platform UI development.
+- **MVVM Architecture**: Maintaining strict separation between UI and business logic.
+- **Clean Code & Clean Architecture**: Focusing on maintainability and inward dependency flow.
+- **Functional Programming in C#**: Embracing immutability and functional patterns.
+- **Reactive Programming**: Expertise in DynamicData and System.Reactive.
+
+## Architectural Principles
+
+- **Pure MVVM**: Mandatory for all UI code. Logic must be independent of UI concerns.
+- **Composition over Inheritance**: Favor modular building blocks over deep inheritance hierarchies.
+- **Inward Dependency Flow**: Abstractions must not depend on implementations.
+- **Immutability**: Prefer immutable structures where practical to ensure predictability.
+- **Stable Public APIs**: Design APIs carefully to ensure long-term stability and clarity.

skills/avalonia-zafiro-development/naming-standards.md

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+# Naming & Coding Standards
+
+## General Standards
+
+- **Explicit Names**: Favor clarity over cleverness.
+- **Async Suffix**: Do **NOT** use the `Async` suffix in method names, even if they return `Task`.
+- **Private Fields**: Do **NOT** use the `_` prefix for private fields.
+- **Static State**: Avoid static state unless explicitly justified and documented.
+- **Method Design**: Keep methods small, expressive, and with low cyclomatic complexity.
+
+## Error Handling
+
+- **Result & Maybe**: Use types from **CSharpFunctionalExtensions** for flow control and error handling.
+- **Exceptions**: Reserved strictly for truly exceptional, unrecoverable situations.
+- **Boundaries**: Never allow exceptions to leak across architectural boundaries.

skills/avalonia-zafiro-development/patterns.md

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+# Common Patterns in Angor/Zafiro
+
+## Refreshable Collections
+
+The `RefreshableCollection` pattern is used to manage lists that can be refreshed via a command, maintaining an internal `SourceCache`/`SourceList` and exposing a `ReadOnlyObservableCollection`.
+
+### Implementation
+
+```csharp
+var refresher = RefreshableCollection.Create(
+        () => GetDataTask(), 
+        model => model.Id)
+    .DisposeWith(disposable);
+
+LoadData = refresher.Refresh;
+Items = refresher.Items;
+```
+
+### Benefits
+- **Automatic Loading**: Handles the command execution and results.
+- **Efficient Updates**: Uses `EditDiff` internally to update items without clearing the list.
+- **UI Friendly**: Exposes `Items` as a `ReadOnlyObservableCollection` suitable for binding.
+
+## Mandatory Validation Pattern
+
+When validating dynamic collections, always use the Zafiro validation extension:
+
+```csharp
+this.ValidationRule(
+        StagesSource
+            .Connect()
+            .FilterOnObservable(stage => stage.IsValid)
+            .IsEmpty(),
+        b => !b,
+        _ => "Stages are not valid")
+    .DisposeWith(Disposables);
+```
+
+## Error Handling Pipeline
+
+Instead of manual `Subscribe`, use `HandleErrorsWith` to pipe errors directly to the user:
+
+```csharp
+LoadProjects.HandleErrorsWith(uiServices.NotificationService, "Could not load projects");
+```

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.