fix(claude-code): install openssh-client for SSH-format commit signing (#111)

The shared `base` stage installs packages with --no-install-recommends,
which drops git's Recommends on ssh-client (provided by openssh-client).
The image therefore ships without ssh-keygen, so any container whose
gitconfig uses SSH-format commit signing (gpg.format=ssh +
commit.gpgsign=true, commonly copied in by VS Code's
dev.containers.copyGitConfig) fails to commit:

    error: cannot run ssh-keygen: No such file or directory

Add openssh-client to the base apt block so both the default and sandbox
targets get ssh-keygen/ssh/ssh-add. It must live in base: the sandbox
firewall blocks deb.debian.org, so it can't be apt-installed at runtime
(same reasoning as chromium). openssh-client hard-depends on libfido2, so
FIDO2 hardware keys (YubiKey sk-ssh-ed25519) sign too, even under
--no-install-recommends.

Closes #110

Author: gatezh

claude-code/.devcontainer/Dockerfile

@@ -55,6 +55,13 @@ ARG GIT_DELTA_VERSION=0.18.2
 # - git: version control
 # - jq: JSON processing (firewall script, onboarding patch)
 # - less: pager for git delta output
+# - openssh-client: provides ssh-keygen, needed for SSH-format commit signing
+#   (gpg.format=ssh + commit.gpgsign=true, copied in via VS Code's
+#   dev.containers.copyGitConfig); also restores ssh/ssh-add. git only
+#   *Recommends* it, so --no-install-recommends drops it unless listed here.
+#   Hard-depends on libfido2, so FIDO2 hardware keys (YubiKey sk-ssh-ed25519)
+#   sign too. Must be in base: the sandbox firewall blocks deb.debian.org, so
+#   it can't be added at runtime (same reasoning as chromium). See issue #110.
 # - sudo: privilege escalation for firewall setup
 RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
     --mount=type=cache,target=/var/lib/apt/lists,sharing=locked \
@@ -67,6 +74,7 @@ RUN --mount=type=cache,target=/var/cache/apt,sharing=locked \
   git \
   jq \
   less \
+  openssh-client \
   sudo
 
 # npm global directory with proper permissions for node user

claude-code/README.md

@@ -17,7 +17,7 @@ Projects consume these pre-built images and control their own tool versions via
 |-------|------|-----|
 | OS | `node:24-trixie-slim` + system packages | Node is needed during the build (Playwright, npm globals) |
 | Shell | Fish, Starship, fzf | Built-in syntax highlighting, autosuggestions, completions |
-| Tools | git-delta, gh CLI, jq, nano, vim, wget, unzip, less, man-db, procps | Standard dev utilities |
+| Tools | git-delta, gh CLI, jq, nano, vim, wget, unzip, less, man-db, procps, openssh-client | Standard dev utilities (`openssh-client` provides `ssh`/`ssh-keygen` — enables SSH-format commit signing) |
 | Mise | The tool manager itself (not the tools) | Projects run `mise install` at container creation for their tool versions |
 | rtk, ralphex | Always-latest from GitHub Releases | Dev infrastructure (like Claude Code) — no version pinning needed in projects |
 | Claude Code | npm global install | npm avoids rate limiting that affects the native installer in parallel CI builds |