Add AI Stack-chan PlatformIO Setup

[meganetaaan]

Summary

Add:

• AI Stack-chan PlatformIO Setup - Video guide for writing AI Stack-chan firmware with PlatformIO.

Category: Videos

Source: extracted from the Stack-chan Cosense crawl and checked for public access before PR creation.

Checklist

• I searched existing entries and confirmed this is not a duplicate.
• I added the item to the appropriate category.
• The link is publicly accessible.
• The description is concise and neutral.
• The entry follows the format: - [Name](URL) - Description.
• This is not my own project.