Added theme switching sample for grid theming topic

samples/grids/grid/grid-theming-overview/App.razor

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+@using IgniteUI.Blazor.Controls
+
+@inject IJSRuntime JS
+
+<div class="container sample ig-typography @(IsDark ? "container--dark" : "")">
+    <div class="options horizontal">
+        <label class="@(IsDark ? "label--dark" : "")">Choose Theme:</label>
+        <select class="theme-select @(IsDark ? "theme-select--dark" : "")"
+                value="@SelectedTheme"
+                @onchange="OnThemeChanged">
+            @foreach (var theme in Themes)
+            {
+                <option value="@theme.Value">@theme.Label</option>
+            }
+        </select>
+    </div>
+    <div class="container fill">
+        <IgbGrid
+        AutoGenerate="false"
+        Data="NwindData"
+        PrimaryKey="ProductID"
+        AllowFiltering="true"
+        Name="grid"
+        @ref="grid">
+            <IgbColumn
+            Field="ProductID"
+            Header="Product ID"
+            Hidden="true">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="ProductName"
+            Header="Product Name"
+            DataType="GridColumnDataType.String"
+            Sortable="true">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="UnitPrice"
+            Header="Unit Price"
+            DataType="GridColumnDataType.Number"
+            Sortable="true">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="QuantityPerUnit"
+            Header="Quantity Per Unit"
+            DataType="GridColumnDataType.String"
+            Sortable="true">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="ReorderLevel"
+            Header="Reorder Level"
+            DataType="GridColumnDataType.Number"
+            Sortable="true">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="Discontinued"
+            Header="Discontinued"
+            DataType="GridColumnDataType.Boolean"
+            Sortable="true"
+            BodyTemplateScript="WebGridBooleanCellTemplate"
+            Name="column1"
+            @ref="column1">
+            </IgbColumn>
+
+            <IgbColumn
+            Field="OrderDate"
+            Header="Order Date"
+            DataType="GridColumnDataType.Date"
+            Sortable="true">
+            </IgbColumn>
+        </IgbGrid>
+    </div>
+</div>
+
+@code {
+
+    private record ThemeOption(string Value, string Label, string CssPath, bool Dark);
+
+    private static readonly ThemeOption[] Themes = new[]
+    {
+        new ThemeOption("light-bootstrap", "Bootstrap (Light)", "_content/IgniteUI.Blazor/themes/grid/light/bootstrap.css", false),
+        new ThemeOption("light-material", "Material (Light)", "_content/IgniteUI.Blazor/themes/grid/light/material.css", false),
+        new ThemeOption("light-fluent", "Fluent (Light)", "_content/IgniteUI.Blazor/themes/grid/light/fluent.css", false),
+        new ThemeOption("light-indigo", "Indigo (Light)", "_content/IgniteUI.Blazor/themes/grid/light/indigo.css", false),
+        new ThemeOption("dark-bootstrap", "Bootstrap (Dark)", "_content/IgniteUI.Blazor/themes/grid/dark/bootstrap.css", true),
+        new ThemeOption("dark-material", "Material (Dark)", "_content/IgniteUI.Blazor/themes/grid/dark/material.css", true),
+        new ThemeOption("dark-fluent", "Fluent (Dark)", "_content/IgniteUI.Blazor/themes/grid/dark/fluent.css", true),
+        new ThemeOption("dark-indigo", "Indigo (Dark)", "_content/IgniteUI.Blazor/themes/grid/dark/indigo.css", true),
+    };
+
+    private string SelectedTheme = "light-bootstrap";
+    private bool IsDark => Themes.FirstOrDefault(t => t.Value == SelectedTheme)?.Dark ?? false;
+
+    private IgbGrid grid;
+    private IgbColumn column1;
+
+    private async Task OnThemeChanged(ChangeEventArgs e)
+    {
+        SelectedTheme = e.Value?.ToString() ?? "light-bootstrap";
+        var theme = Themes.FirstOrDefault(t => t.Value == SelectedTheme);
+        if (theme != null)
+        {
+            await JS.InvokeVoidAsync("eval", $"document.getElementById('grid-theme').href = '{theme.CssPath}'");
+        }
+    }
+
+    private NwindData _nwindData = null;
+    public NwindData NwindData
+    {
+        get
+        {
+            if (_nwindData == null)
+            {
+                _nwindData = new NwindData();
+            }
+            return _nwindData;
+        }
+    }
+
+}

samples/grids/grid/grid-theming-overview/BlazorClientApp.csproj

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+<Project Sdk="Microsoft.NET.Sdk.BlazorWebAssembly">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <RazorLangVersion>3.0</RazorLangVersion>
+    <AssemblyName>Infragistics.Samples</AssemblyName>
+    <RootNamespace>Infragistics.Samples</RootNamespace>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
+    <NoWarn>1701;1702,IDE0028,BL0005,0219,CS1998</NoWarn>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="IgniteUI.Blazor.Trial" Version="25.2.38" />
+    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="10.0.1" />
+    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.DevServer" Version="10.0.1" />
+    <PackageReference Include="System.Net.Http.Json" Version="10.0.1" />
+  </ItemGroup>
+
+</Project>

samples/grids/grid/grid-theming-overview/BlazorClientApp.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.29613.14
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "BlazorClientApp", "BlazorClientApp.csproj", "{F69CC3F0-BCD1-4CE6-9F39-CBED14E7FA78}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{F69CC3F0-BCD1-4CE6-9F39-CBED14E7FA78}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F69CC3F0-BCD1-4CE6-9F39-CBED14E7FA78}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F69CC3F0-BCD1-4CE6-9F39-CBED14E7FA78}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F69CC3F0-BCD1-4CE6-9F39-CBED14E7FA78}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {FC52AAC8-4488-40AE-9621-75F6BA744B18}
+	EndGlobalSection
+EndGlobal