Document and automate xxxx-xx validation workflow

[bgyss]

Summary

• expand xxxx validation notes, automation ideas, and cross-references across specs, docs, and README entries, including the new real XCI intake guide and capture helper script
• advance XCI handling and validation plumbing throughout the pipeline, CLI, and validation crates with added samples and helper scripts
• add validation artifacts, workflows, and dependencies so future automation can pick up where this work leaves off

Testing

• Not run (not requested)