docs(authors): list restored AI-authoring meta-tutorials (#2374)

[jung-thomas]

Companion doc update for #2374. The tutorial content itself is restored in meta-tutorials-Contribution#11.

Changes to docs/authors/meta-tutorials.md

• Adds §7 "AI-assisted authoring" to the recommended path, listing the three restored tutorials (AutoAuthor incl. the [AUTOAUTHOR_VIDEO_*] variant, CodeCheck, Validate) with QA-channel links.
• Replaces the "three slugs are stale (404)" caveat with a restoration note pointing at the content PR; keeps the "may still 404 until the QA rebuild" warning so authors aren't surprised in the interim.

Merge order: this can merge independently, but the §7 links only resolve after the content PR merges and the QA channel rebuilds.