feat(settings): Add AppVersionSettings for app-specific version tracking

- Create AppVersionSettings class to store application version independently from PleasantUI library version
- Add Version, VersionType, and VersionLabel properties with DataMember serialization support
- Include VersionTypeDescription computed property for display-friendly release channel names
- Register AppVersionSettings in PleasantSettingsGenerationContext for JSON source generation
- Add AppVersion property to PleasantSettings with null validation and initialization
- Enables applications to manage their own versioning semantics separate from the UI framework

Author: pieckenst

src/PleasantUI/Core/GenerationContexts/PleasantSettingsGenerationContext.cs

@@ -4,4 +4,5 @@ namespace PleasantUI.Core.GenerationContexts;
 
 [JsonSourceGenerationOptions(WriteIndented = true)]
 [JsonSerializable(typeof(PleasantSettings))]
+[JsonSerializable(typeof(PleasantUI.Core.Settings.AppVersionSettings))]
 internal partial class PleasantSettingsGenerationContext : JsonSerializerContext;

src/PleasantUI/Core/PleasantSettings.cs

@@ -57,6 +57,7 @@ public class PleasantSettings : ViewModelBase
     private string _language = "en";
 
     private WindowSettings _windowSettings;
+    private AppVersionSettings _appVersion;
 
     /// <summary>
     /// Gets the singleton instance of the PleasantSettings class.
@@ -199,12 +200,33 @@ public AvaloniaList<uint> ColorPalettes
         set => SetProperty(ref _colorPalettes, value);
     }
 
+    // ── App-specific version (separate from PleasantUI library version) ────────
+
+    /// <summary>
+    /// Gets or sets application-specific version information.
+    /// Use this to store and display your app's own version, release channel,
+    /// and version label — independently of the PleasantUI library version.
+    /// </summary>
+    [DataMember]
+    public AppVersionSettings AppVersion
+    {
+        get => _appVersion;
+        set
+        {
+            if (value is null)
+                throw new NullReferenceException("AppVersion is null");
+
+            SetProperty(ref _appVersion, value);
+        }
+    }
+
     /// <summary>
     /// Initializes a new instance of the <see cref="PleasantSettings"/> class 
     /// with default window and render settings.
     /// </summary>
     public PleasantSettings()
     {
         _windowSettings = new WindowSettings();
+        _appVersion = new AppVersionSettings();
     }
 }

src/PleasantUI/Core/Settings/AppVersionSettings.cs

@@ -0,0 +1,66 @@
+using System.Runtime.Serialization;
+
+namespace PleasantUI.Core.Settings;
+
+/// <summary>
+/// Stores application-specific version information inside <see cref="PleasantSettings"/>.
+/// Reuses <see cref="PleasantVersionType"/> for release-channel semantics while keeping
+/// app versioning fully separate from the PleasantUI library version.
+/// </summary>
+public class AppVersionSettings : ViewModelBase
+{
+    private string _version = string.Empty;
+    private PleasantVersionType _versionType = PleasantVersionType.Stable;
+    private string _versionLabel = "Version";
+
+    /// <summary>
+    /// Gets or sets the application version string (e.g., "1.0.0", "2.3.1-beta").
+    /// </summary>
+    [DataMember]
+    public string Version
+    {
+        get => _version;
+        set => SetProperty(ref _version, value);
+    }
+
+    /// <summary>
+    /// Gets or sets the release channel / version type for the application.
+    /// Reuses <see cref="PleasantVersionType"/> — Stable, BugFix, Alpha, Beta, RC, Canary.
+    /// </summary>
+    [DataMember]
+    public PleasantVersionType VersionType
+    {
+        get => _versionType;
+        set
+        {
+            if (SetProperty(ref _versionType, value))
+                RaisePropertyChanged(nameof(VersionTypeDescription));
+        }
+    }
+
+    /// <summary>
+    /// Gets or sets a custom label shown next to the version string (e.g., "Version", "App Version").
+    /// Defaults to "Version".
+    /// </summary>
+    [DataMember]
+    public string VersionLabel
+    {
+        get => _versionLabel;
+        set => SetProperty(ref _versionLabel, value);
+    }
+
+    /// <summary>
+    /// Gets a display-friendly description of <see cref="VersionType"/>.
+    /// Derived — not serialized.
+    /// </summary>
+    public string VersionTypeDescription => VersionType switch
+    {
+        PleasantVersionType.Stable           => "Stable Release",
+        PleasantVersionType.BugFix           => "Bug Fix Release",
+        PleasantVersionType.Alpha            => "Alpha Pre-Release",
+        PleasantVersionType.Beta             => "Beta Pre-Release",
+        PleasantVersionType.ReleaseCandidate => "Release Candidate",
+        PleasantVersionType.Canary           => "Canary Build",
+        _                                    => "Unknown"
+    };
+}