feat: add Launcher Next .NET 8 foundation

Launcher.Next.App/App.xaml

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+<Application x:Class="Launcher.Next.App.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" StartupUri="MainWindow.xaml" />

Launcher.Next.App/App.xaml.cs

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+namespace Launcher.Next.App; public partial class App : System.Windows.Application { }

Launcher.Next.App/Launcher.Next.App.csproj

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+<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><OutputType>WinExe</OutputType><TargetFramework>net8.0-windows</TargetFramework><UseWPF>true</UseWPF><EnableWindowsTargeting>true</EnableWindowsTargeting></PropertyGroup><ItemGroup><ProjectReference Include="..\Launcher.Next.Application\Launcher.Next.Application.csproj" /><ProjectReference Include="..\Launcher.Next.Observability\Launcher.Next.Observability.csproj" /></ItemGroup></Project>

Launcher.Next.App/MainWindow.xaml

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+<Window x:Class="Launcher.Next.App.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Launcher Next (Foundation)" Height="300" Width="540"><StackPanel Margin="20"><TextBlock FontSize="20" Text="Launcher Next — foundation"/><TextBlock Margin="0,12,0,0" Text="Plant 3D: discovery available in diagnostics"/><TextBlock Text="Mode: Legacy (default); NextPilot requires explicit configuration"/><TextBlock Text="Package: no production catalog connected"/><Button Margin="0,16,0,0" IsEnabled="False" Content="Launch (disabled: dry-run foundation)"/></StackPanel></Window>

Launcher.Next.App/MainWindow.xaml.cs

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+namespace Launcher.Next.App; public partial class MainWindow : System.Windows.Window { public MainWindow() => InitializeComponent(); }