chore: scaffold WPF app and integration test projects

- TeamsISO.App: hand-rolled net8.0-windows WPF csproj since the WPF
  template isn't shipped on linux-arm64 .NET SDK; UI is a placeholder
  for Phase C.
- TeamsISO.Engine.IntegrationTests: cross-platform xunit project with a
  skipped scaffold fact tagged [Trait("requires", "ndi")] for Phase B.
- TeamsISO.Linux.slnf: solution filter for non-Windows CI that excludes
  the WPF project (which can only build on Windows).

TeamsISO.Linux.slnf

@@ -0,0 +1,11 @@
+{
+  "solution": {
+    "path": "TeamsISO.sln",
+    "projects": [
+      "src/TeamsISO.Engine/TeamsISO.Engine.csproj",
+      "src/TeamsISO.Engine.NdiInterop/TeamsISO.Engine.NdiInterop.csproj",
+      "src/tests/TeamsISO.Engine.Tests/TeamsISO.Engine.Tests.csproj",
+      "src/tests/TeamsISO.Engine.IntegrationTests/TeamsISO.Engine.IntegrationTests.csproj"
+    ]
+  }
+}

TeamsISO.sln

@@ -13,6 +13,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{DBDF4A1D
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.Tests", "src\tests\TeamsISO.Engine.Tests\TeamsISO.Engine.Tests.csproj", "{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.App", "src\TeamsISO.App\TeamsISO.App.csproj", "{80DCE039-3BBC-4D3F-B44B-51F324591C29}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "TeamsISO.Engine.IntegrationTests", "src\tests\TeamsISO.Engine.IntegrationTests\TeamsISO.Engine.IntegrationTests.csproj", "{A85E331D-026E-4BDE-B89C-0CC4C95001CE}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -34,11 +38,21 @@ Global
 		{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{80DCE039-3BBC-4D3F-B44B-51F324591C29}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{80DCE039-3BBC-4D3F-B44B-51F324591C29}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{80DCE039-3BBC-4D3F-B44B-51F324591C29}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{80DCE039-3BBC-4D3F-B44B-51F324591C29}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A85E331D-026E-4BDE-B89C-0CC4C95001CE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A85E331D-026E-4BDE-B89C-0CC4C95001CE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A85E331D-026E-4BDE-B89C-0CC4C95001CE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A85E331D-026E-4BDE-B89C-0CC4C95001CE}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(NestedProjects) = preSolution
 		{F0D24EAE-9225-4DC4-B3D2-6966077287A0} = {46E05E34-8A87-4986-87D3-FE0DE4E05F44}
 		{E737E54B-73DE-4F74-909C-1F0F5CF82AC6} = {46E05E34-8A87-4986-87D3-FE0DE4E05F44}
 		{DBDF4A1D-4215-42D5-B456-2CE7159DF848} = {46E05E34-8A87-4986-87D3-FE0DE4E05F44}
 		{F8DBD7AB-E160-4B75-88FC-BAECDD4D44E8} = {DBDF4A1D-4215-42D5-B456-2CE7159DF848}
+		{80DCE039-3BBC-4D3F-B44B-51F324591C29} = {46E05E34-8A87-4986-87D3-FE0DE4E05F44}
+		{A85E331D-026E-4BDE-B89C-0CC4C95001CE} = {DBDF4A1D-4215-42D5-B456-2CE7159DF848}
 	EndGlobalSection
 EndGlobal

src/TeamsISO.App/App.xaml

@@ -0,0 +1,6 @@
+<Application x:Class="TeamsISO.App.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources/>
+</Application>

src/TeamsISO.App/App.xaml.cs

@@ -0,0 +1,7 @@
+using System.Windows;
+
+namespace TeamsISO.App;
+
+public partial class App : Application
+{
+}

src/TeamsISO.App/MainWindow.xaml

@@ -0,0 +1,10 @@
+<Window x:Class="TeamsISO.App.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        Title="TeamsISO" Height="600" Width="900">
+    <Grid>
+        <TextBlock Text="TeamsISO — Phase A scaffold (UI implemented in Phase C)"
+                   HorizontalAlignment="Center" VerticalAlignment="Center"
+                   FontSize="16" Foreground="#444"/>
+    </Grid>
+</Window>

src/TeamsISO.App/MainWindow.xaml.cs

@@ -0,0 +1,11 @@
+using System.Windows;
+
+namespace TeamsISO.App;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}

src/TeamsISO.App/TeamsISO.App.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <UseWPF>true</UseWPF>
+    <RootNamespace>TeamsISO.App</RootNamespace>
+    <!-- WPF only builds on Windows. Non-Windows CI skips this project. -->
+    <BuildOnNonWindows Condition="'$(OS)' != 'Windows_NT'">false</BuildOnNonWindows>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\TeamsISO.Engine\TeamsISO.Engine.csproj" />
+    <ProjectReference Include="..\TeamsISO.Engine.NdiInterop\TeamsISO.Engine.NdiInterop.csproj" />
+  </ItemGroup>
+
+</Project>

src/tests/TeamsISO.Engine.IntegrationTests/IntegrationTestsScaffold.cs

@@ -0,0 +1,11 @@
+namespace TeamsISO.Engine.IntegrationTests;
+
+public class IntegrationTestsScaffold
+{
+    [Fact(Skip = "Phase A: integration tests require NDI runtime — added in Phase B.")]
+    [Trait("requires", "ndi")]
+    public void ScaffoldFactSkipsCleanly()
+    {
+        Assert.True(true);
+    }
+}

src/tests/TeamsISO.Engine.IntegrationTests/TeamsISO.Engine.IntegrationTests.csproj

@@ -0,0 +1,29 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.0" />
+    <PackageReference Include="FluentAssertions" Version="6.12.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="xunit" Version="2.5.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\TeamsISO.Engine\TeamsISO.Engine.csproj" />
+    <ProjectReference Include="..\..\TeamsISO.Engine.NdiInterop\TeamsISO.Engine.NdiInterop.csproj" />
+  </ItemGroup>
+
+</Project>