Add Swift coding agent tutorial series - #933

What is this?

• Title: Build a Coding Agent from Scratch in Swift
• URL: https://ivanmagda.dev/posts/s00-bootstrapping-the-project
• Section: Swift

I guide readers through nine stages that produce a working Claude Code-style coding agent in Swift. Each article links to the source for its stage, and I publish the companion project under the MIT license at https://github.com/ivan-magda/swift-coding-agent.

Checklist

• This PR adds one multi-part tutorial series.
• Readers can access the series without a paywall, login, or newsletter signup.
• Readers build a complete working artifact by following the series.
• I searched README.md for the URL and title and found no existing entry.
• I used the nested multi-part series format under the Swift section.
• I used direct URLs.
• I ran python3 scripts/check_readme.py lint; it exits 0 with no errors or warnings.
• I am the author of the tutorial and the companion repository.