[Bug] CLI validator ignores SubWorkflowNode in reachability and summary output

[alxsuv]

Symptom
$ hensu validate main-research --with sub-summarizer -d working-dir
[OK] Workflow is valid!
Name: main-research
Nodes: 4
Agents: 2
[WARN] Unreachable nodes: done, publish

Two defects observed when validating a workflow composed with --with :

1. False unreachable warning. done and publish are reachable in the composed graph (they sit downstream of the injected SubWorkflowNode exit transitions) yet the validator flags them as orphaned.
2. Summary hides composition. The output makes no mention of sub-summarizer. Nodes: 4 and Agents: 2 reflect only the parent workflow — nested nodes and agents contributed by the sub-workflow are invisible to the
   user.

Acceptance

• Validating main-research --with sub-summarizer produces no false unreachable warnings.
• Validator output makes the composed sub-workflow visible, including its own node and agent counts.
• Regression coverage for reachability and summary rendering across composition boundaries.