feat: install Claude Code with its native installer in dev containers

[mjun0812]

Overview and Background

The generated dev container now installs Claude Code with Anthropic's native installer during the image build and no longer contains Node.js. Previously Claude Code came from the ghcr.io/anthropics/devcontainer-features/claude-code feature, which installs the npm package and therefore needs Node.js. On Ubuntu 26.04 the feature's own Node.js fallback failed, so #33 had to add the node feature explicitly, reintroducing a runtime that #19 had deliberately removed when Codex switched to its standalone installer.

Related Issues

None. Follows up on #33 and restores the intent of #19.

Implementation Approach

• The native installer (curl -fsSL https://claude.ai/install.sh | bash) downloads a checksum-verified binary and installs it under $HOME (~/.local/share/claude/versions/<v> with a ~/.local/bin/claude launcher). It is run as the vscode user in the Dockerfile so the files belong to the user that will run it; the transient ~/.claude/downloads directory is removed afterwards.
• /usr/local/bin/claude is a symlink to the user's launcher so the command works from bash -lc, zsh -lc, and non-login shells without relying on rc files that the common-utils feature rewrites.
• The claude-code and node features are removed from devcontainer.json. github-cli and common-utils stay.
• The host ~/.claude bind mount (authentication and config) is unaffected: the binary lives in ~/.local, and the image was verified with an empty ~/.claude mounted over it.

Changes

• template/.devcontainer/Dockerfile: native Claude Code install as vscode, symlink in /usr/local/bin.
• template/.devcontainer/devcontainer.json: node and claude-code features removed.
• README.md, template/README.md: rebuilding the image updates both Claude Code and Codex.

Impact

• User-facing: claude is available exactly as before. The image no longer ships Node.js or npm; projects that need Node.js for their own work should add the node feature themselves.
• Updates: Claude Code is fetched at image build time (latest release), the same policy as Codex. The native binary can also self-update inside a running container because it owns ~/.local/share/claude.
• Build time: the feature step that installed Node.js and the npm package is replaced by a single binary download.

Validation Results

Generated a Python 3.14 project from this branch and built the dev container both with plain Docker and with the Dev Container CLI (features included).

# Plain Dockerfile build; empty ~/.claude mounted to mimic the host bind mount
docker build -f .devcontainer/Dockerfile -t demo-cc-plain .
docker run --rm --user vscode --tmpfs /home/vscode/.claude demo-cc-plain bash -c \
  'claude --version; readlink -f /usr/local/bin/claude; command -v node || echo "node: absent"'
# 2.1.263 (Claude Code)
# /home/vscode/.local/share/claude/versions/2.1.263
# node: absent
docker run --rm demo-cc-plain bash -c 'claude --version'   # 2.1.263 (Claude Code) as root too

# Full build with features
npx -y @devcontainers/cli build --workspace-folder . --image-name demo-cc-full
docker run --rm --user vscode --tmpfs /home/vscode/.claude demo-cc-full zsh -lc \
  'claude --version; gh --version | head -1; command -v node || echo "node: absent"'
# 2.1.263 (Claude Code) / gh version 2.100.0 / node: absent
docker run --rm --user vscode demo-cc-full bash -lc 'claude --version; codex --version; uv --version'
# 2.1.263 (Claude Code) / codex-cli 0.153.4 / uv 0.12.10