chore(scaffold): add solution skeleton for App, Ui, Data, Worker and tests

Create .slnx with five projects, wire references (App->Ui->Data,
Worker->Data, Tests->Worker+Data), install Avalonia/MVVM/SignalR.Client/
Sqlite/Hosting packages, and add schema.sql per docs/plan.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/ClaudeDo.Ui.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <ItemGroup>
+    <ProjectReference Include="..\ClaudeDo.Data\ClaudeDo.Data.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="12.0.0" />
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.1" />
+    <PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="8.0.11" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
+  </PropertyGroup>
+
+</Project>

src/ClaudeDo.Ui/ViewModels/MainWindowViewModel.cs

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+namespace ClaudeDo.Ui.ViewModels;
+
+public partial class MainWindowViewModel : ViewModelBase
+{
+    public string Greeting { get; } = "Welcome to Avalonia!";
+}

src/ClaudeDo.Ui/ViewModels/ViewModelBase.cs

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+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace ClaudeDo.Ui.ViewModels;
+
+public abstract class ViewModelBase : ObservableObject
+{
+}

src/ClaudeDo.Ui/Views/MainWindow.axaml

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+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:ClaudeDo.Ui.ViewModels"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+        x:Class="ClaudeDo.Ui.Views.MainWindow"
+        x:DataType="vm:MainWindowViewModel"
+        Icon="/Assets/avalonia-logo.ico"
+        Title="ClaudeDo.App">
+
+    <Design.DataContext>
+        <!-- This only sets the DataContext for the previewer in an IDE,
+             to set the actual DataContext for runtime, set the DataContext property in code (look at App.axaml.cs) -->
+        <vm:MainWindowViewModel/>
+    </Design.DataContext>
+
+    <TextBlock Text="{Binding Greeting}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+
+</Window>

src/ClaudeDo.Ui/Views/MainWindow.axaml.cs

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+using Avalonia.Controls;
+
+namespace ClaudeDo.Ui.Views;
+
+public partial class MainWindow : Window
+{
+    public MainWindow()
+    {
+        InitializeComponent();
+    }
+}