🚀 Feature: redirect blog.joshuakgoldberg.com -> joshuakgoldberg.com/blog

### Bug Report Checklist

- [X] I have tried restarting my IDE and the issue persists.
- [X] I have pulled the latest `main` branch of the repository.
- [X] I have [searched for related issues](https://github.com/JoshuaKGoldberg/dot-com/issues?q=is%3Aissue) and found none that matched my issue.

### Overview

Hey Josh,

Didn't realize that you had completely migrated to the new blog since fixing your RSS feed last year e.g. https://github.com/JoshuaKGoldberg/Goldblog/pull/392

New blog looks great! I'll need to get my RSS feed pointed at the new one and catch up on all this content

Would it be possible / have you thought about redirecting from the old blog subdomain to the new blog subdirectory?

e.g., if you did an HTTP 301 redirect of `blog.joshuakgoldberg.com/*` -> `joshuakgoldberg.com/blog/:splat` I _think_ that would cover most things based on a quick sanity check of blog posts that exist on both e.g. `https://blog.joshuakgoldberg.com/speeding-up-centered-part-1-81-iframe-embeds/` -> `https://www.joshuakgoldberg.com/blog/speeding-up-centered-part-1-81-iframe-embeds/`

I'm starting the redirect recommendation since that'll help humans _and_ computers equally. If that's not possible, maybe just updating the contents of blog.joshuakgoldberg.com to reflect the new content location?

### Additional Info

_No response_