ci(release): build + publish the roboco-agent-grok image

Add roboco-agent-grok to the release workflow's image build/publish map so
registry deploys carry the Grok runtime image (parity with every other
agent image). Split from the feature commit because pushing a workflow
change requires a workflow-scoped token.

.github/workflows/release.yml

@@ -77,7 +77,7 @@ jobs:
             done
           }
 
-          # agent-base MUST build first: the eight agent images build
+          # agent-base MUST build first: the agent images build
           # `FROM roboco-agent-base` — a local tag that has to exist in the daemon
           # before they build. Tag it locally (for the FROM) and for both registries.
           echo "::group::build roboco-agent-base"
@@ -100,6 +100,7 @@ jobs:
             [roboco-agent-prompter]=docker/agent-prompter.Dockerfile
             [roboco-agent-secretary]=docker/agent-secretary.Dockerfile
             [roboco-agent-pr-reviewer]=docker/agent-pr-reviewer.Dockerfile
+            [roboco-agent-grok]=docker/agent-grok.Dockerfile
           )
           for name in "${!IMAGES[@]}"; do
             echo "::group::build ${name}"