Add Windows app icon

[Balragon]

Summary

• Add iMirror icon assets for Windows app branding.
• Wire the icon into the executable, WPF window, and Inno installer setup executable.
• Update the changelog with validation notes.

Validation

• dotnet build .\iMirror.sln -c Release
• dotnet test .\MacMirrorReceiver.Tests\MacMirrorReceiver.Tests.csproj -c Release
• Extracted the associated icon from the built iMirror.exe successfully.