launcher: QR code + share buttons on host ready panel

The single Copy button left it on the user to format a message and
get the code into Discord/email. Added a layout that makes sharing
obvious:

- QR encodes the join code text so a friend with a phone can scan
  the host's screen and forward the code without typing it
- "Copy as message" formats a one-line "Join {server} on DorkNet!
  Download at github.com/... and paste this code:" pitch
- "Email to friend" opens the default mail client with subject +
  body prefilled, code in the body
- QR built via QRCoder -> WriteableBitmap directly (no
  System.Drawing dependency); palette matches the launcher

launcher/Backend/QrCodeRenderer.cs

@@ -0,0 +1,60 @@
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using QRCoder;
+
+namespace DorkNet.Launcher.Backend;
+
+/// <summary>Turns a join-code string into a WPF <see cref="BitmapSource"/>
+/// using QRCoder's raw module matrix. We render the matrix directly to a
+/// <see cref="WriteableBitmap"/> rather than going through PNG bytes so we
+/// avoid pulling in System.Drawing.Common (Windows-only, slated for
+/// trimming in cross-platform .NET).
+///
+/// <para>Colour choice matches the launcher palette: white (Ink) modules
+/// on the deep purple-navy (BgDeeper) background so the QR is legible
+/// against the dark panel.</para></summary>
+public static class QrCodeRenderer
+{
+    public static BitmapSource Render(string text, int pixelSize = 220)
+    {
+        // QRCodeGenerator -> QRCodeData (matrix of bools) -> WriteableBitmap.
+        using var gen = new QRCodeGenerator();
+        using var data = gen.CreateQrCode(text, QRCodeGenerator.ECCLevel.M);
+        var modules = data.ModuleMatrix;
+        var moduleCount = modules.Count;
+        if (moduleCount == 0)
+            throw new InvalidOperationException("QR generation produced an empty matrix.");
+
+        // Scale up to the requested pixel size — int division so each
+        // module is an exact pixel count (avoids subpixel blur). Quiet
+        // zone (4-module margin) is part of QRCodeData already.
+        var moduleSize = Math.Max(1, pixelSize / moduleCount);
+        var dim = moduleCount * moduleSize;
+
+        var bmp = new WriteableBitmap(dim, dim, 96, 96, PixelFormats.Bgra32, null);
+        var stride = dim * 4;
+        var pixels = new byte[dim * stride];
+
+        // Light pixel = Ink (#F7F3FF), dark pixel = BgDeeper (#0E0A1F).
+        // Order is BGRA in the buffer.
+        var light = new byte[] { 0xFF, 0xF3, 0xF7, 0xFF };
+        var dark = new byte[] { 0x1F, 0x0A, 0x0E, 0xFF };
+
+        for (int y = 0; y < moduleCount; y++)
+        for (int x = 0; x < moduleCount; x++)
+        {
+            var on = modules[y][x];
+            var src = on ? dark : light;
+            for (int py = 0; py < moduleSize; py++)
+            for (int px = 0; px < moduleSize; px++)
+            {
+                var offset = ((y * moduleSize + py) * stride) + ((x * moduleSize + px) * 4);
+                Buffer.BlockCopy(src, 0, pixels, offset, 4);
+            }
+        }
+
+        bmp.WritePixels(new System.Windows.Int32Rect(0, 0, dim, dim), pixels, stride, 0);
+        bmp.Freeze();
+        return bmp;
+    }
+}

launcher/DorkNet.Launcher.csproj

@@ -20,4 +20,11 @@
        The Backend/* classes (release downloader, server process, etc.) are
        UI-framework-agnostic and stay unchanged from the PhotinoNET draft. -->
 
+  <ItemGroup>
+    <!-- QR rendering for the share panel — generates the code as raw
+         module bytes, MainWindow draws it onto a WPF Image. No System.Drawing
+         dependency that way, so it stays portable. -->
+    <PackageReference Include="QRCoder" Version="1.6.0" />
+  </ItemGroup>
+
 </Project>

launcher/MainWindow.xaml

@@ -235,16 +235,36 @@
                             </StackPanel>
                         </Border>
 
-                        <!-- Join code -->
+                        <!-- Join code panel — appears once the host is up.
+                             QR encodes the same code text; friends can
+                             scan with a phone to grab it without typing. -->
                         <Border x:Name="JoinCodePanel" Visibility="Collapsed"
                                 Style="{StaticResource Panel}"
                                 Background="{StaticResource CardBgHost}">
                             <StackPanel>
                                 <TextBlock Style="{StaticResource SectionTitle}"
                                            Text="🎉 Share this with friends" />
-                                <DockPanel>
+
-                                    <Button DockPanel.Dock="Right" Style="{StaticResource PrimaryBtn}"
+                                <Grid>
-                                            Content="Copy" Click="OnCopyJoinCode" Margin="10,0,0,0" />
+                                    <Grid.ColumnDefinitions>
+                                        <ColumnDefinition Width="Auto" />
+                                        <ColumnDefinition Width="*" />
+                                    </Grid.ColumnDefinitions>
+
+                                    <Border Grid.Column="0" Background="White"
+                                            CornerRadius="10" Padding="8"
+                                            VerticalAlignment="Top"
+                                            Margin="0,0,16,0">
+                                        <Image x:Name="JoinCodeQrImage"
+                                               Width="180" Height="180"
+                                               RenderOptions.BitmapScalingMode="NearestNeighbor"
+                                               SnapsToDevicePixels="True"
+                                               UseLayoutRounding="True" />
+                                    </Border>
+
+                                    <StackPanel Grid.Column="1">
+                                        <TextBlock Style="{StaticResource FieldLabel}"
+                                                   Text="JOIN CODE" />
                                         <Border Background="{StaticResource BgDeeper}"
                                                 BorderBrush="{StaticResource Border}" BorderThickness="1"
                                                 CornerRadius="10" Padding="12,10">
@@ -253,10 +273,25 @@
                                                      Background="Transparent" BorderThickness="0"
                                                      TextWrapping="Wrap" />
                                         </Border>
-                                </DockPanel>
+
+                                        <WrapPanel Margin="0,12,0,0">
+                                            <Button Style="{StaticResource PrimaryBtn}"
+                                                    Content="Copy code" Click="OnCopyJoinCode" />
+                                            <Button Style="{StaticResource Btn}"
+                                                    Content="Copy as message"
+                                                    Click="OnCopyJoinCodeMessage"
+                                                    Margin="10,0,0,0" />
+                                            <Button Style="{StaticResource Btn}"
+                                                    Content="Email to friend"
+                                                    Click="OnEmailJoinCode"
+                                                    Margin="10,0,0,0" />
+                                        </WrapPanel>
+
                                         <TextBlock Foreground="{StaticResource InkFaint}" FontSize="11"
-                                           Text="Paste this in their DorkNet launcher's Join screen."
+                                                   TextWrapping="Wrap" Margin="0,12,0,0"
-                                           Margin="0,8,0,0" />
+                                                   Text="Your friend opens DorkNet, picks &quot;Join a friend&quot;, and pastes the code. The QR encodes the same text — handy for getting it onto a phone for forwarding." />
+                                    </StackPanel>
+                                </Grid>
                             </StackPanel>
                         </Border>
                     </StackPanel>

launcher/MainWindow.xaml.cs

@@ -331,6 +331,7 @@ public partial class MainWindow : Window
                 Name = _state.ServerName,
             });
             JoinCodeText.Text = code;
+            JoinCodeQrImage.Source = QrCodeRenderer.Render(code);
             JoinCodePanel.Visibility = Visibility.Visible;
             HostStatusText.Text = _state.HostingMode == HostingMode.LocalNetwork
                 ? $"Hosting on your local network at {_hostApex}. Share the join code with friends on the same WiFi."
@@ -408,6 +409,38 @@ public partial class MainWindow : Window
         catch (Exception ex) { ShowError("Copy failed: " + ex.Message); }
     }
 
+    private void OnCopyJoinCodeMessage(object sender, RoutedEventArgs e)
+    {
+        var name = string.IsNullOrWhiteSpace(_state.ServerName)
+            ? "my DorkNet server"
+            : _state.ServerName;
+        var msg =
+            $"Join {name} on DorkNet! Grab the launcher at " +
+            "https://github.com/DorkSquadRR/DorkNet and paste this code:\n\n" +
+            JoinCodeText.Text;
+        try { Clipboard.SetText(msg); }
+        catch (Exception ex) { ShowError("Copy failed: " + ex.Message); }
+    }
+
+    private void OnEmailJoinCode(object sender, RoutedEventArgs e)
+    {
+        var name = string.IsNullOrWhiteSpace(_state.ServerName)
+            ? "my DorkNet server"
+            : _state.ServerName;
+        // mailto: body is URL-encoded; Uri.EscapeDataString handles
+        // the newlines + code text without trashing slashes or =.
+        var subject = Uri.EscapeDataString($"Join {name} on DorkNet");
+        var body = Uri.EscapeDataString(
+            $"Hey! Want to play on {name}?\n\n" +
+            "1. Download the DorkNet launcher: https://github.com/DorkSquadRR/DorkNet\n" +
+            "2. Open it and pick \"Join a friend\"\n" +
+            "3. Paste this code:\n\n" +
+            JoinCodeText.Text);
+        try { Process.Start(new ProcessStartInfo($"mailto:?subject={subject}&body={body}")
+            { UseShellExecute = true }); }
+        catch (Exception ex) { ShowError("Email failed: " + ex.Message); }
+    }
+
     // ── Join flow ───────────────────────────────────────────────────────
     private void OnJoinCodeInputChanged(object sender, TextChangedEventArgs e)
         => RefreshJoinReadiness();