feat: implement Phase 1 — solution skeleton and domain model

Creates the 9-project .NET 8 solution (5 src + 4 test) with Marathon.Domain
fully implemented: value objects (SportCode, EventId, OddsRate, OddsValue,
BetScope hierarchy), enums (Side, BetType, OddsSource, AnomalyKind), and
entities (Sport, Country, League, Event, Bet, OddsSnapshot, EventResult,
Anomaly) with all invariants enforced in constructors. 96 domain tests pass
(FluentAssertions + xUnit). Directory.Build.props and Directory.Packages.props
centralise build settings and NuGet versions. Both Marathon.sln and Marathon.slnx
are committed; dotnet build Marathon.sln succeeds with 0 warnings/errors.

src/Marathon.Hosts.WpfBlazor/App.xaml

@@ -0,0 +1,9 @@
+<Application x:Class="Marathon.Hosts.WpfBlazor.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:Marathon.Hosts.WpfBlazor"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+         
+    </Application.Resources>
+</Application>

src/Marathon.Hosts.WpfBlazor/App.xaml.cs

@@ -0,0 +1,10 @@
+using System.Windows;
+
+namespace Marathon.Hosts.WpfBlazor;
+
+/// <summary>
+/// Interaction logic for App.xaml
+/// </summary>
+public partial class App : System.Windows.Application
+{
+}

src/Marathon.Hosts.WpfBlazor/AssemblyInfo.cs

@@ -0,0 +1,10 @@
+using System.Windows;
+
+[assembly:ThemeInfo(
+    ResourceDictionaryLocation.None,            //where theme specific resource dictionaries are located
+                                                //(used if a resource is not found in the page,
+                                                // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly   //where the generic resource dictionary is located
+                                                //(used if a resource is not found in the page,
+                                                // app, or any theme specific resource dictionaries)
+)]

src/Marathon.Hosts.WpfBlazor/MainWindow.xaml

@@ -0,0 +1,12 @@
+<Window x:Class="Marathon.Hosts.WpfBlazor.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:Marathon.Hosts.WpfBlazor"
+        mc:Ignorable="d"
+        Title="MainWindow" Height="450" Width="800">
+    <Grid>
+
+    </Grid>
+</Window>

src/Marathon.Hosts.WpfBlazor/MainWindow.xaml.cs

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+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+
+namespace Marathon.Hosts.WpfBlazor;
+
+/// <summary>
+/// Interaction logic for MainWindow.xaml
+/// </summary>
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}

src/Marathon.Hosts.WpfBlazor/Marathon.Hosts.WpfBlazor.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\Marathon.UI\Marathon.UI.csproj" />
+    <ProjectReference Include="..\Marathon.Infrastructure\Marathon.Infrastructure.csproj" />
+    <ProjectReference Include="..\Marathon.Application\Marathon.Application.csproj" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+</Project>