launcher: rewrite as native WPF, drop PhotinoNET/WebView2

Initial v0.1 (commit df9dac0) used PhotinoNET wrapping WebView2 + HTML/JS,
but rendered as a blank window on first run — WebView2 + file:// URI
quirks. Switching to native WPF: built into the .NET 9 Windows SDK
(no NuGet), single-file self-contained publish, instant window open.

All Backend/*.cs orchestration logic carried over unchanged (they're
UI-framework-agnostic). Replaced:
- Program.cs (PhotinoNET bootstrap) -> App.xaml(.cs) + MainWindow.xaml(.cs)
- ui/index.html + style.css + app.js -> MainWindow.xaml (XAML views) +
  App.xaml resource styles
- Backend/MessageBridge.cs (JS<->C# router) -> direct method calls in
  MainWindow.xaml.cs code-behind

RecRoomPicker now uses Microsoft.Win32.OpenFolderDialog (added in .NET 8)
instead of WinForms FolderBrowserDialog — keeps the project WPF-only.
Backend files needed explicit 'using System.IO;' since the WPF SDK
doesn't include it in implicit usings.

launcher/DorkNet.Launcher.csproj

@@ -5,7 +5,7 @@
     <TargetFramework>net9.0-windows</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
-    <UseWindowsForms>true</UseWindowsForms>
+    <UseWPF>true</UseWPF>
     <RootNamespace>DorkNet.Launcher</RootNamespace>
     <AssemblyName>dorknet</AssemblyName>
     <ApplicationManifest>app.manifest</ApplicationManifest>
@@ -16,20 +16,8 @@
     <EnableCompressionInSingleFile>true</EnableCompressionInSingleFile>
   </PropertyGroup>
 
-  <ItemGroup>
-    <!-- PhotinoNET wraps WebView2 with a tiny .NET host. The WebView2 runtime
-         ships in Windows 11 + modern Windows 10 (Edge auto-installs it). -->
-    <PackageReference Include="Photino.NET" Version="4.0.16" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <!-- UI assets get copied next to the binary at publish time so the
-         PhotinoNET window can load them from disk. Keeps the binary
-         smaller than embedding base64; the user can also patch the UI
-         in-place without rebuilding the .exe. -->
-    <None Update="ui\**\*">
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </None>
-  </ItemGroup>
+  <!-- WPF is built into the .NET 9 Windows SDK; no NuGet package needed.
+       The Backend/* classes (release downloader, server process, etc.) are
+       UI-framework-agnostic and stay unchanged from the PhotinoNET draft. -->
 
 </Project>