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

scripts/lib/cli-catalog.mjs

@@ -55,9 +55,36 @@ export function agentImageNpmPackages(catalog) {
   return packages;
 }
 
-/** The `--build-arg` pairs the agent image takes. PURE. */
-export function agentImageBuildArgPairs(catalog) {
-  return [['CLI_NPM_PACKAGES', agentImageNpmPackages(catalog).join(' ')]];
+/**
+ * Environment variable → agent.Dockerfile ARG for the optional git-host CLIs (gh, az).
+ * ⚠️ Mirrored by `GIT_HOST_CLI_BUILD_ARGS` in `src/docker-hosts.ts`; the parity test pins them.
+ */
+export const GIT_HOST_CLI_BUILD_ARGS = [
+  ['CODEMAN_AGENT_IMAGE_INSTALL_GH', 'CODEMAN_INSTALL_GH'],
+  ['CODEMAN_AGENT_IMAGE_INSTALL_AZ', 'CODEMAN_INSTALL_AZ'],
+];
+
+/**
+ * The `--build-arg` pairs for the optional git-host CLIs. PURE. An unset or empty variable
+ * contributes NOTHING, so the Dockerfile's own default (off) applies and the argv is the same
+ * as before these existed; anything other than 0/1 is refused rather than guessed at.
+ */
+export function gitHostCliBuildArgPairs(env) {
+  const pairs = [];
+  for (const [envName, argName] of GIT_HOST_CLI_BUILD_ARGS) {
+    const value = env[envName];
+    if (value === undefined || value === '') continue;
+    if (value !== '0' && value !== '1') {
+      throw new Error(`${envName} must be 0 or 1, got ${JSON.stringify(value)}`);
+    }
+    pairs.push([argName, value]);
+  }
+  return pairs;
+}
+
+/** The `--build-arg` pairs the agent image takes. PURE given `env`. */
+export function agentImageBuildArgPairs(catalog, env = process.env) {
+  return [['CLI_NPM_PACKAGES', agentImageNpmPackages(catalog).join(' ')], ...gitHostCliBuildArgPairs(env)];
 }
 
 /** Read the committed catalogue. IO. */