Add a changelog to the cli-design agent skill for clig baseline additions

[kergoth]

What

Add a structured changelog to the cli-design agent skill (home/dot_agents/skills/cli-design/) tracking changes/additions relative to the clig (Command Line Interface Guidelines) baseline it's built on.

Why

The skill already has a "Beyond clig" section in its docs, but as the skill gets refined over time, a more structured changelog would make it easier to see what's been added or changed and why, versus the original clig baseline.

Scope

• cli-design is not a workflow skill — it covers guidelines that apply everywhere, not personal preferences or workflow-specific guidance. Personal preferences belong in guidance or a wrapper skill instead.
• Changelog entries should be additions that address gaps in the original clig baseline only, not personal-preference or workflow-specific additions.

Done when

• A changelog mechanism exists in the skill (format TBD — e.g. a CHANGELOG.md in the skill directory, or a structured section within existing docs) that records baseline-gap additions going forward.
• Existing "Beyond clig" content is reconciled with or migrated into the new changelog structure as appropriate.