wip: Windows desktop app scaffold (WinUI 3/.NET 8) + NSIS installer + docs

Owner decision pending (STATE.md DC-100 tick): adopt/ship/park.
Preserved from fragile git stash to named branch 2026-08-23.
NOTE: requires a Windows build machine (WinUI XAML compiler + MSIX do not
cross-build on Linux) — see WINDOWS_APP_BUILD.md in this tree.
Secret-scanned clean 2026-08-23 (no keys/tokens/PEM in tree).

desktop/DashCaddy.Desktop.csproj

@@ -0,0 +1,47 @@
+<Project Sdk="Microsoft.Windows.Sdk">
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0-windows10.0.19041.0</TargetFramework>
+    <TargetPlatformMinVersion>10.0.19041.0</TargetPlatformMinVersion>
+    <SupportedOSPlatformVersion>10.0.19041.0</SupportedOSPlatformVersion>
+    <UseWinUI>true</UseWinUI>
+    <EnableMsixTooling>true</EnableMsixTooling>
+    <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained>
+    <PublishProfile>Properties\PublishProfiles\win10-$(Platform).pubxml</PublishProfile>
+    <ApplicationIcon>Assets\dashcaddy.ico</ApplicationIcon>
+    <AssemblyName>DashCaddy</AssemblyName>
+    <RootNamespace>DashCaddy.Desktop</RootNamespace>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.6.240628000" />
+    <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.26100.1742" />
+    <PackageReference Include="Docker.DotNet" Version="3.125.15" />
+    <PackageReference Include="System.Text.Json" Version="9.0.0" />
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />
+    <PackageReference Include="Serilog" Version="4.2.0" />
+    <PackageReference Include="Serilog.Sinks.File" Version="6.0.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="appsettings.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+  <ItemGroup>
+    <Content Include="Assets\**" CopyToOutputDirectory="PreserveNewest" />
+  </ItemGroup>
+
+  <!-- MSIX Packaging -->
+  <PropertyGroup>
+    <AppxPackageDir>$(OutDir)AppxPackages\</AppxPackageDir>
+    <AppxBundle>Always</AppxBundle>
+    <AppxBundlePlatforms>x64|arm64</AppxBundlePlatforms>
+    <GenerateAppInstallerFile>True</GenerateAppInstallerFile>
+    <AppInstallerUri>https://dashcaddy.net/installer/</AppInstallerUri>
+    <HoursBetweenUpdateChecks>4</HoursBetweenUpdateChecks>
+  </PropertyGroup>
+</Project>