feat: Add Golang support with new image variant and CLI integration

[meijeran]

This pull request adds Golang support to the project by introducing a new standalone Golang Docker image variant, updating the CLI to support the new image via flags, and enhancing documentation and CI/CD workflows accordingly. It follows the established approach used for Rust support, ensuring consistency and ease of use.

Golang image support and CLI integration:

• Added a new Dockerfile (docker/variants/Dockerfile.golang) to build the Golang variant, installing Go 1.25.5 and configuring the workspace for all users.
• Updated the CLI (app/Commands/Run/RunCommand.cs, app/Program.cs) to support a new --golang (-go) flag and PowerShell-style alias, including image tag selection logic.
• Added golang to the list of available image tags in the CLI image listing command (app/Commands/Images/ListImages.cs).

CI/CD and workflow updates:

• Modified GitHub Actions workflow (.github/workflows/publish.yml) to build and publish the Golang image, and to include it in the build summary.

Documentation improvements:

• Updated README.md and docs/docker-images.md to document the new Golang image, CLI flags, use cases, and build dependency diagrams.
• Added a detailed task file summarizing the implementation and testing steps (docs/tasks/20260114-01-add-golang-support.md).

Version updates:

• Bumped version numbers to 2026.01.14 across all relevant files to reflect the new release.

This update enables users to easily select a Go development environment using the CLI, and ensures the new image is documented, tested, and built as part of the standard workflow.