fix(docker): merge-time fixes for #492

- test: the complete-identity case now checks the combined
  agentImageBuildArgPairs() argv on both producers, so the manual
  build-agent-image.mjs path cannot drop the identity unnoticed
- both producers: GIT_IDENTITY_BUILD_ARGS carries the mirror/parity
  warning its gh/az neighbour has
- the partial-identity error names CODEMAN_AGENT_IMAGE_GIT_USER_NAME and
  CODEMAN_AGENT_IMAGE_GIT_USER_EMAIL; test regex follows
- wiki Docker-Cases: mention the identity variables next to the gh/az
  switches

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

scripts/lib/cli-catalog.mjs

@@ -64,7 +64,10 @@ export const GIT_HOST_CLI_BUILD_ARGS = [
   ['CODEMAN_AGENT_IMAGE_INSTALL_AZ', 'CODEMAN_INSTALL_AZ'],
 ];
 
-/** Environment variables passed through to the agent image's system Git configuration. */
+/**
+ * Environment variable → Dockerfile ARG for the image's system Git identity.
+ * ⚠️ Mirrored by `GIT_IDENTITY_BUILD_ARGS` in `src/docker-hosts.ts`; the parity test pins them.
+ */
 export const GIT_IDENTITY_BUILD_ARGS = [
   ['CODEMAN_AGENT_IMAGE_GIT_USER_NAME', 'GIT_USER_NAME'],
   ['CODEMAN_AGENT_IMAGE_GIT_USER_EMAIL', 'GIT_USER_EMAIL'],
@@ -94,7 +97,8 @@ export function gitIdentityBuildArgPairs(env) {
   const configured = pairs.filter(([, value]) => value !== '');
   if (configured.length === 0) return [];
   if (configured.length !== pairs.length) {
-    throw new Error('Git user name and email must both be set when configuring Git identity');
+    const names = GIT_IDENTITY_BUILD_ARGS.map(([envName]) => envName).join(' and ');
+    throw new Error(`${names} must both be set when configuring Git identity`);
   }
   return pairs;
 }