Add CSC (Composite Scene) editor - #371

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v2, actions/setup-dotnet@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Possible null reference return.

Possible null reference return.

Possible null reference return.

Possible null reference return.

Possible null reference return.

Possible null reference return.

Possible null reference return.

Possible null reference return.

Cannot convert null literal to non-nullable reference type.