Add converter for dark theme SVG usage.

Aaru.Gui/App.xaml

@@ -34,7 +34,11 @@
 <Application xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:localization="clr-namespace:Aaru.Localization;assembly=Aaru.Localization"
+             xmlns:helpers="clr-namespace:Aaru.Gui.Helpers"
              x:Class="Aaru.Gui.App">
+    <Application.Resources>
+        <helpers:ThemeToSvgPathConverter x:Key="ThemeToSvgPathConverter" />
+    </Application.Resources>
     <Application.Styles>
         <FluentTheme /> <StyleInclude Source="avares://Avalonia.Controls.DataGrid/Themes/Fluent.xaml" />
         <!-- TODO: Abandoned project need to find replacement

Aaru.Gui/Helpers/ThemeToSvgPathConverter.cs

@@ -0,0 +1,77 @@
+// /***************************************************************************
+// Aaru Data Preservation Suite
+// ----------------------------------------------------------------------------
+//
+// Filename       : ThemeToSvgPathConverter.cs
+// Author(s)      : Natalia Portillo <claunia@claunia.com>
+//
+// Component      : GUI helpers.
+//
+// --[ Description ] ----------------------------------------------------------
+//
+//     Converter to provide theme-aware SVG asset paths.
+//
+// --[ License ] --------------------------------------------------------------
+//
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General public License as
+//     published by the Free Software Foundation, either version 3 of the
+//     License, or (at your option) any later version.
+//
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General public License for more details.
+//
+//     You should have received a copy of the GNU General public License
+//     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// ----------------------------------------------------------------------------
+// Copyright © 2011-2025 Natalia Portillo
+// ****************************************************************************/
+
+#nullable enable
+
+using System;
+using System.Globalization;
+using Avalonia.Data.Converters;
+using Avalonia.Styling;
+
+namespace Aaru.Gui.Helpers;
+
+/// <summary>
+///     Converter that returns different SVG asset paths based on the current theme (light or dark).
+/// </summary>
+/// <inheritdoc />
+public class ThemeToSvgPathConverter : IValueConverter
+{
+    /// <inheritdoc />
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if(value is not ThemeVariant themeVariant || parameter is not string fullPath) return null;
+
+        // Check if it's dark theme
+        bool isDark = themeVariant == ThemeVariant.Dark;
+
+        if(!isDark) return fullPath;
+
+        // For dark theme, insert "Dark/" before the filename
+        int lastSlashIndex = fullPath.LastIndexOf('/');
+
+        if(lastSlashIndex == -1)
+        {
+            // No path separator, just filename
+            return $"Dark/{fullPath}";
+        }
+
+        // Split path and filename, insert Dark/ before filename
+        string directory = fullPath[..(lastSlashIndex + 1)];
+        string filename  = fullPath[(lastSlashIndex   + 1)..];
+
+        return $"{directory}Dark/{filename}";
+    }
+
+    /// <inheritdoc />
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) =>
+        throw new NotImplementedException();
+}