feat(docker): replace Packer snapshots with Docker-based agent delivery (#2206)

* feat(docker): replace Packer snapshots with Docker-based agent delivery

Docker images on GHCR are public and cross-account, unlike DO snapshots
which are private/account-scoped. Cloud-init installs Docker + pulls the
agent image during boot. The install step extracts pre-built binaries via
`docker cp` and falls back to normal install if unavailable.

- Add Dockerfiles for all 7 agents (claude, codex, openclaw, opencode,
  kilocode, zeroclaw, hermes)
- Convert docker.yml to matrix build for all agents
- Add tryInstallFromDocker() shared helper with Docker-first install
- Add Docker pull to DigitalOcean cloud-init userdata
- Remove Packer snapshot pipeline, lookup, and SSH-only wait
- Remove packer/ directory (HCL templates, tier scripts, agents.json)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* security: address review findings in docker agent delivery

- Add agentName validation regex (/^[a-z0-9-]+$/) in digitalocean.ts
  before interpolation into cloud-init script
- Quote dockerImage variable in all docker command strings in
  agent-setup.ts to prevent command injection
- Restrict docker cp to specific known directories (.claude, .bun,
  .local, .npm, .cargo, .opencode) instead of blanket /root/.

Agent: pr-maintainer
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: B <6723574+louisgv@users.noreply.github.com>

sh/docker/codex.Dockerfile

@@ -0,0 +1,17 @@
+FROM ubuntu:24.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+# Base packages
+RUN apt-get update -y && \
+    apt-get install -y --no-install-recommends \
+      curl git ca-certificates build-essential unzip zsh && \
+    rm -rf /var/lib/apt/lists/*
+
+# Node.js 22 via n
+RUN curl --proto '=https' -fsSL https://raw.githubusercontent.com/tj/n/master/bin/n | bash -s install 22
+
+# Codex CLI
+RUN npm install -g @openai/codex
+
+CMD ["/bin/sleep", "inf"]