Add Tesserae.Playground.Host with H5 Compiler Service

[theolivenbaum]

This PR introduces the Tesserae.Playground.Host project, which serves as a backend for the Tesserae Playground. It leverages the H5.Compiler.Service to compile user-submitted C# code into JavaScript and HTML compatible with the H5 runtime.

Key features implemented:

• CompilerService: Handles the orchestration of creating a temporary project, configuring the H5.Translator, downloading necessary NuGet packages (h5, h5.core, h5.Target), and invoking the compilation process.
• Custom SDK Resolution: Implements a strategy to layout SDKs (including h5.Target and system .NET SDKs) in a temporary directory and configures MSBuildSDKsPath to enable the H5.Compiler.Service to resolve build targets correctly.
• API Endpoint: Provides a POST /compile endpoint that accepts C# source and returns the generated JavaScript and index.html.

This submission represents the current progress on the Host implementation, specifically addressing the complex dependency and SDK resolution requirements of hosting the H5 compiler. The Tesserae.Playground.FrontEnd project is planned for the next phase.

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PR created automatically by Jules for task 10862351439595950420 started by @theolivenbaum

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