feat: initial project structure with Snake.Core, CLI and Avalonia skeleton

Snake.Avalonia/App.axaml

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+<Application xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="Snake.Avalonia.App"
+             RequestedThemeVariant="Default">
+             <!-- "Default" ThemeVariant follows system theme variant. "Dark" or "Light" are other available options. -->
+
+    <Application.Styles>
+        <FluentTheme />
+    </Application.Styles>
+</Application>

Snake.Avalonia/App.axaml.cs

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+using Avalonia;
+using Avalonia.Controls.ApplicationLifetimes;
+using Avalonia.Markup.Xaml;
+
+namespace Snake.Avalonia;
+
+public partial class App : Application
+{
+    public override void Initialize()
+    {
+        AvaloniaXamlLoader.Load(this);
+    }
+
+    public override void OnFrameworkInitializationCompleted()
+    {
+        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+        {
+            desktop.MainWindow = new MainWindow();
+        }
+
+        base.OnFrameworkInitializationCompleted();
+    }
+}

Snake.Avalonia/MainWindow.axaml

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+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:views="using:Snake.Avalonia.Views"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        x:Class="Snake.Avalonia.MainWindow"
+        Title="Snake">
+    <views:GameView />
+</Window>

Snake.Avalonia/MainWindow.axaml.cs

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+using Avalonia.Controls;
+
+namespace Snake.Avalonia;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}

Snake.Avalonia/Program.cs

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+using Avalonia;
+using System;
+
+namespace Snake.Avalonia;
+
+class Program
+{
+    // Initialization code. Don't use any Avalonia, third-party APIs or any
+    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
+    // yet and stuff might break.
+    [STAThread]
+    public static void Main(string[] args) => BuildAvaloniaApp()
+        .StartWithClassicDesktopLifetime(args);
+
+    // Avalonia configuration, don't remove; also used by visual designer.
+    public static AppBuilder BuildAvaloniaApp()
+        => AppBuilder.Configure<App>()
+            .UsePlatformDetect()
+#if DEBUG
+            .WithDeveloperTools()
+#endif
+            .WithInterFont()
+            .LogToTrace();
+}

Snake.Avalonia/Snake.Avalonia.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ApplicationManifest>app.manifest</ApplicationManifest>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="12.0.4" />
+    <PackageReference Include="Avalonia.Desktop" Version="12.0.4" />
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="12.0.4" />
+    <PackageReference Include="Avalonia.Fonts.Inter" Version="12.0.4" />
+    <PackageReference Include="AvaloniaUI.DiagnosticsSupport" Version="2.2.1">
+      <IncludeAssets Condition="'$(Configuration)' != 'Debug'">None</IncludeAssets>
+      <PrivateAssets Condition="'$(Configuration)' != 'Debug'">All</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Snake.Core\Snake.Core.csproj" />
+  </ItemGroup>
+</Project>

Snake.Avalonia/Views/GameView.axaml

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+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="Snake.Avalonia.Views.GameView">
+    <TextBlock Text="Snake game UI — connect Snake.Core here"
+               HorizontalAlignment="Center"
+               VerticalAlignment="Center" />
+</UserControl>

Snake.Avalonia/Views/GameView.axaml.cs

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+using Avalonia.Controls;
+
+namespace Snake.Avalonia.Views;
+
+/// <summary>
+/// Placeholder for the Avalonia game view.
+/// Wire up <see cref="Snake.Core.SnakeGame"/> here for rendering and input.
+/// </summary>
+public partial class GameView : UserControl
+{
+    public GameView()
+    {
+        InitializeComponent();
+    }
+}

Snake.Avalonia/app.manifest

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+<?xml version="1.0" encoding="utf-8"?>
+<assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1">
+  <!-- This manifest is used on Windows only.
+       Don't remove it as it might cause problems with window transparency and embedded controls.
+       For more details visit https://learn.microsoft.com/en-us/windows/win32/sbscs/application-manifests -->
+  <assemblyIdentity version="1.0.0.0" name="Snake.Avalonia.Desktop"/>
+
+  <compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
+    <application>
+      <!-- A list of the Windows versions that this application has been tested on
+           and is designed to work with. Uncomment the appropriate elements
+           and Windows will automatically select the most compatible environment. -->
+
+      <!-- Windows 10 -->
+      <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}" />
+    </application>
+  </compatibility>
+</assembly>