Modernize Solitaire UI, animations, and WebAssembly startup

[jmacato]

Updates Solitaire to .NET 10 and the Avalonia public nightly.

• Move gold-button effects, lighting controls, and animation definitions into XAML.
• Replace handwritten Avalonia properties with built-in source generators.
• Improve card movement, shadows, navigation, and narrow-screen layouts.
• Add a WebAssembly loading screen with progress and retry support.
• Update platform projects, build workflows, and convert the solution to .slnx.

Validation: Desktop and Browser Release builds pass with no warnings. All 11 local regression suites pass.