refactor(code-server): install Docker CLI, plugins and gh into home

- Drop the Docker and GitHub apt repositories and the Ruby build headers
  from the image; keep build-essential, bubblewrap, zip and unzip.
- Document home installs for the Docker CLI with its Compose and Buildx
  plugins, gh, Go, Rust, Python, Node and Java, ordered so each installer
  writes to ~/.zshrc and SDKMAN stays last.
- Drop the Ruby, GitLab CLI and jq instructions.

code-server/Dockerfile

@@ -6,30 +6,6 @@ USER root
 RUN apt-get update \
   && apt-get install -y --no-install-recommends \
     build-essential bubblewrap unzip zip \
-    libffi-dev libssl-dev libyaml-dev zlib1g-dev \
-  && rm -rf /var/lib/apt/lists/*
-
-# Docker CLI with the Compose and Buildx plugins, from Docker's apt repository,
-# and GitHub CLI, from GitHub's apt repository.
-RUN install -m 0755 -d /etc/apt/keyrings \
-  && curl -fsSL https://download.docker.com/linux/debian/gpg \
-    -o /etc/apt/keyrings/docker.asc \
-  && curl -fsSL https://cli.github.com/packages/githubcli-archive-keyring.gpg \
-    -o /etc/apt/keyrings/githubcli-archive-keyring.gpg \
-  && chmod a+r /etc/apt/keyrings/docker.asc /etc/apt/keyrings/githubcli-archive-keyring.gpg \
-  && printf '%s\n' \
-    'Types: deb' \
-    'URIs: https://download.docker.com/linux/debian' \
-    "Suites: $(. /etc/os-release && echo "$VERSION_CODENAME")" \
-    'Components: stable' \
-    "Architectures: $(dpkg --print-architecture)" \
-    'Signed-By: /etc/apt/keyrings/docker.asc' \
-    > /etc/apt/sources.list.d/docker.sources \
-  && echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main" \
-    > /etc/apt/sources.list.d/github-cli.list \
-  && apt-get update \
-  && apt-get install -y --no-install-recommends \
-    docker-ce-cli docker-buildx-plugin docker-compose-plugin gh \
   && rm -rf /var/lib/apt/lists/*
 
 # Workspace directory, owned by the container user.