Docs: Undocumented feature `@agent-output-style-setup`

Issue Title: Docs: Undocumented feature @agent-output-mode-setup

Body:

Hello Claude Code Team,

First off, thanks for the excellent work on this tool!

I've discovered a very useful but currently undocumented feature: the @agent-output-mode-setup command. This feature allows users to generate a set of pre-defined output modes, which is a powerful way to customize the agent's response style for different tasks. Since it's not in the documentation, it's completely undiscoverable for most users.

How to Reproduce

1. In the Claude Code CLI, run the command: @agent-output-mode-setup
2. The agent runs a setup process and displays the following confirmation upon completion:

```
⏺ The output mode setup is complete! I've created 4 example output modes for you:

1. Concise - Brief, action-focused responses
2. Educational - Detailed explanations with learning insights
3. Code Reviewer - Structured code analysis
4. Rapid Prototyping - Fast iteration focused

These are now available in ~/.claude/output-modes/. You can select them through Claude Code's interface or create your own custom
modes using the template provided.
```

1. This creates a new directory ~/.claude/output-modes/ and populates it with four template files:

• concise.md
• code-reviewer.md
• educational.md
• rapid-prototyping.md

Example Generated File (concise.md)

Here is the content of one of the generated files to show what they look like:

---
name: Concise
description: Brief, action-focused responses with minimal explanations
---

Keep responses brief and to the point. Focus on actionable steps over detailed explanations.

Response guidelines:
- Use bullet points for clarity
- Limit explanations to essential information only
- Prioritize code and commands over prose
- Skip background context unless specifically requested
- Aim for responses under 200 words when possible

When providing solutions:
- Lead with the direct answer
- Include only necessary steps
- Use short, clear sentences
- Omit "why" explanations unless asked

Suggested Action

This is a fantastic feature that greatly enhances the usability of Claude Code. Could you please add it to the official documentation?

It would be helpful to document:

• The existence of the @agent-output-mode-setup command.
• The location of the generated files (~/.claude/output-modes/).
• How users can select or switch between these modes via the CLI or interface.
• Instructions on how users can create their own custom .md output modes based on the generated templates.

Adding this to the documentation would help many users tailor the tool to their specific workflows.

Thanks for your consideration