Add Portfolio

Add a new portfolio project page based on the user's input.

Steps

1. Parse the user's input from $ARGUMENTS to extract:

   • Project name
   • GitHub repo URL
   • Demo URL (if provided)
   • YouTube video URL (if provided, extract the video ID for embedding)
   • Project description / summary
   • Feature list

2. Determine sidebar_position: Read all existing docs/*.md files, find the highest sidebar_position value, and use the next number.

3. Generate the filename: Convert the project name to kebab-case for the filename (e.g., "Multiplayer Piano" → multiplayer-piano.md).

4. Create docs/<filename>.md using this template:

---
sidebar_position: <next_position>
---

# <Project Name>

<One-line summary>

- **Demo**: <demo_url>
- **Source Code**: <github_url>

## Demo

<iframe width="100%" style={{aspectRatio: '16/9'}} src="https://www.youtube.com/embed/<video_id>" title="<Project Name> Demo" frameBorder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowFullScreen></iframe>

## About

<Description paragraph>

## Features

- <feature 1>
- <feature 2>
- ...