feat(branding): add app and installer icons

- app: ClaudeTask.ico wired as ApplicationIcon and MainWindow.Icon
  via avares URI
- installer: ClaudeTaskSetup.ico wired as ApplicationIcon and embedded
  as a WPF Resource so WizardWindow and SettingsWindow can reference it
  via pack URI

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

src/ClaudeDo.App/ClaudeDo.App.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ApplicationManifest>app.manifest</ApplicationManifest>
+    <ApplicationIcon>Assets\ClaudeTask.ico</ApplicationIcon>
     <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
   </PropertyGroup>