feat(docker): opt-in gh + az CLIs with git credential helpers for private repos

Add Case -> Clone Repo could only reach public repositories in the Docker
deployment. This lets a deployment opt in to the GitHub CLI and the Azure
CLI (+ azure-devops extension) as git credential helpers. Codeman itself
still collects no credentials.

- server.Dockerfile / agent.Dockerfile: CODEMAN_INSTALL_GH /
  CODEMAN_INSTALL_AZ build args (0 or 1, default 0; anything else stops the
  build). Off leaves no apt repository, package, extension, helper script
  or credential entry, so a default build is unchanged. On installs from
  the vendors' apt repositories and configures system gitconfig helpers:
  github.com / gist.github.com -> `gh auth git-credential`, dev.azure.com /
  *.visualstudio.com -> new docker/git-credential-azure-cli (an Entra ID
  token from `az account get-access-token`, or AZURE_DEVOPS_EXT_PAT).
  A helper whose CLI is not signed in prints nothing, so a private clone
  still fails fast.
- The extension lives in AZURE_EXTENSION_DIR outside HOME
  (/opt/codeman-az-extensions, runtime-owned; /opt/az-extensions, gid-0
  group-writable in the agent image).
- Hosts turn them on in docker-compose.override.yml: `build: args:` for the
  server image, `environment:` CODEMAN_AGENT_IMAGE_INSTALL_GH / _AZ for the
  agent image. build-agent-image.mjs and the in-app auto-build share one
  env -> ARG table (pinned by the parity test) and pass nothing when unset.
  docker-compose.yaml is untouched; .env.example only gains a comment, so
  the self-updater's environment gate sees no new keys.
- Docker cases seed the gh sign-in (~/.config/gh/hosts.yml, config.yml) and
  the az sign-in files from ~/.azure per file, read-only, like pi/grok.
- The Clone Repo AUTH_REQUIRED message says how to sign the server's git
  in instead of claiming private repositories cannot be cloned.
- Docs: docker/README.md "Private repositories", docker-compose.md,
  docker-cases.md, the Quick-Start / Core-Concepts / Docker-Cases wiki
  pages, security-architecture.md, architecture-invariants.md, changeset.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0167CiuzLrmjYWxwKp3rMWjw

.changeset/git-host-auth-clis.md

@@ -0,0 +1,5 @@
+---
+"aicodeman": minor
+---
+
+Docker images: optional GitHub CLI and Azure CLI for private GitHub and Azure DevOps repositories. Both are opt-in and off by default. Build the server image with `CODEMAN_INSTALL_GH=1` / `CODEMAN_INSTALL_AZ=1` (under `build: args:` in `docker/docker-compose.override.yml`) to add `gh` and/or `az` with the `azure-devops` extension, plus system Git credential helpers that route github.com through `gh auth git-credential` and dev.azure.com / *.visualstudio.com through a new `az`-backed helper (`docker/git-credential-azure-cli`, which also honours `AZURE_DEVOPS_EXT_PAT`). Sign the CLIs in once from a shell session and Add Case → Clone Repo can clone private repositories; until then a private clone still fails fast with an authentication error. The Docker-case agent image takes the same switches from `CODEMAN_AGENT_IMAGE_INSTALL_GH` / `_AZ` (the `environment:` of the override file, or in front of `build-agent-image.mjs`), and a seeded Docker case now also copies the `gh` sign-in (`~/.config/gh/hosts.yml`, `config.yml`) and the `az` sign-in files from `~/.azure` into its container, read-only and per file like the other CLIs. The Clone Repo authentication error now says how to sign the server's git in instead of claiming private repositories cannot be cloned. This changes `server.Dockerfile`, so Compose deployments need a `Start-Codeman.sh` rebuild rather than an in-app update; with neither switch set the rebuilt image is unchanged.