Phase 3: app icon (multi-resolution ICO + master PNG)

scripts/generate-icons.ps1 renders the icon programmatically with
System.Drawing - rounded teal square (#0E7C66) with a stylized white
hook glyph - at 16/24/32/48/64/128/256 px and assembles a proper
multi-resolution Microsoft ICO. The PNG and ICO outputs land in
resources/. The script is the source of truth; re-run after editing
the design.

GUI csproj uses ApplicationIcon for the EXE icon and embeds the .ico
+ .png as Resources so MainWindow and AboutDialog can use them via
WPF's resource URI scheme.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/WebhookServer.Gui/Views/AboutDialog.xaml

@@ -2,9 +2,10 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Title="About Webhook Server"
-        Height="320" Width="420"
+        Height="360" Width="440"
         ResizeMode="NoResize"
         WindowStartupLocation="CenterOwner"
+        Icon="/webhook-server.ico"
         ShowInTaskbar="False">
     <Grid Margin="20">
         <Grid.RowDefinitions>