Display Plugin name after skill name when using /skills command to display skill list

### Describe the feature or problem you'd like to solve

In skill list, it is not easily tell which plugin install the skill, currently it only shows (Copilot) vs (Plugin)

### Proposed solution

In the skill list, showing the name of actual plugin that installed this skill.

So, the skill list will display skill like:
[] brainstorming (superpowers) Use when you have a written implementation plan to execute in...

### Example prompts or workflows

/skills

### Additional context

_No response_

Start at the /skills command entry point and trace how each skill is formatted in the list. Identify where the current Copilot-versus-Plugin label is selected, then check the existing command tests or fixtures for skill-list output. Done means the installed plugin name appears after the skill name, as in the proposed example, without breaking existing entries.

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