Run on a runtime image that exists

[woksin]

Summary

The published image can now be pulled and started.

Fixed

• Container image builds again: it named a .NET 10 runtime tag that does not exist, so the first release published no image at all (P-26).

[woksin]

The v0.1.0 publish failed at docker/build-push-action with mcr.microsoft.com/dotnet/aspnet:10.0-bookworm-slim: not found. There is no Debian-slim runtime variant for .NET 10 — those tags stop at 9.0 — so the tag never resolved. 10.0-noble is what Studio's services run on, so this follows the house convention rather than picking a new one.

Verified locally: docker build -f Docker/Dockerfile succeeds, and docker run on the result starts the app and stops exactly where it should with no configuration — the Cratis:Prompter:Discord:Token startup validation from P-42. That exercises the runtime image, the publish output and the entrypoint together.

The v0.1.0 release and tag exist but have no image behind them; merging this cuts v0.1.1, which will be the first version with a pullable image.