Switch base image to the Go 1.25 Bookworm devcontainer and rework container tooling installs. Remove explicit apt/pip installs from the old image and instead remove the expired Yarn repo key, install Azure CLI, Helm, kubectl, Argo CD CLI, and Google Cloud SDK (including GKE auth plugin). Update devcontainer metadata: change container name, add --privileged to runArgs, and refresh the VS Code extensions list to include Go/Helm/AKS/Azure tooling and Copilot.
