fix: Pin csharp-ls to exact NuGet version in Docker builds

[GordonBeeming]

Summary

• Resolve the actual latest csharp-ls version from the NuGet API in the prepare-versions CI job, matching the pattern used for copilot, playwright, and dotnet SDK versions
• Pass CSHARP_LS_VERSION as a build arg to all Docker images that use the lsp-csharp snippet (dotnet, dotnet-10, dotnet-playwright, dotnet-rust)
• Change the Dockerfile ARG default from latest to 0.22.0 for deterministic local builds

Test plan

• CI prepare-versions job resolves a real version from NuGet API
• dotnet and dotnet-10 image builds succeed (previously failing)
• dotnet-playwright and dotnet-rust image builds succeed
• verify-generated-dockerfiles job passes

Generated with Claude Code and GitButler

[Copilot]

Pull request overview

This PR makes Docker image builds deterministic and reliable by ensuring csharp-ls is installed with an explicit NuGet version (instead of latest) and wiring CI to resolve and pass that exact version into relevant image builds.

Changes:

• Pin CSHARP_LS_VERSION default in the lsp-csharp Docker snippet to 0.22.0 (avoids invalid dotnet tool install --version latest).
• Extend the prepare-versions workflow job to resolve the latest csharp-ls version from NuGet and expose it as a job output.
• Pass CSHARP_LS_VERSION build-arg to all generated Docker images that include the lsp-csharp snippet (dotnet, dotnet-10, dotnet-playwright, dotnet-rust).

Reviewed changes

Copilot reviewed 2 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
docker/snippets/lsp-csharp.Dockerfile	Changes CSHARP_LS_VERSION default from latest to a concrete version for deterministic installs.
docker/generated/Dockerfile.dotnet	Updates embedded snippet ARG default to 0.22.0 (generated output stays consistent).
docker/generated/Dockerfile.dotnet-10	Updates embedded snippet ARG default to 0.22.0 (generated output stays consistent).
docker/generated/Dockerfile.dotnet-playwright	Updates embedded snippet ARG default to 0.22.0 (generated output stays consistent).
docker/generated/Dockerfile.dotnet-rust	Updates embedded snippet ARG default to 0.22.0 (generated output stays consistent).
.github/workflows/publish.yml	Resolves csharp-ls version from NuGet, plumbs it through job outputs, and injects it as a Docker build-arg for affected images.