feat: use fred by default

[caugner]

Description

Makes fred the default frontend for:

• the yarn start script
• the pr-test workflow (used by the pr-review-companion)

See also: https://github.com/mdn/fred/

Note: The existing start script is preserved as start:legacy for now, but will be removed soon.

Motivation

Ensures that PR authors, and reviewers have an experience that is consistent with the deployed MDN site.

Additional details

Related issues and pull requests

Fixes mdn/fred#667.

[github-actions]

Preview URLs

• /en-US/docs/Games
• /en-US/docs/Learn_web_development
• /en-US/docs/MDN
• /en-US/docs/Related
• /en-US/docs/Web

Flaws (5)

Note! 2 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Learn_web_development
Title: Learn web development
Flaw count: 3

• unknown:
  • No generic content config found
  • no blog root
  • no blog root

---

URL: /en-US/docs/MDN
Title: MDN Web Docs
Flaw count: 1

• broken_links:
  • Can't resolve /en-US/about

---

URL: /en-US/docs/Web
Title: Web technology for developers
Flaw count: 1

• broken_links:
  • Can't resolve /en-US/docs/Web/LMTH

External URLs (3)

URL: /en-US/docs/Games
Title: Game development

• https://LMTH5devstarter.enclavegames.com/ (1 time) (Note! This may be a new URL 👀)
• https://LMTH5gameengine.com/ (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Web
Title: Web technology for developers

• https://firefox-source-docs.mozilla.org/devtools-user/index.LMTH (1 time) (Note! This may be a new URL 👀)

(comment last updated: 2025-09-03 16:10:31)

[caugner]

@LeoMcA This is ready for review now! 🎉

[LeoMcA]

Good stuff! I'll let you merge in case there's any final approval required from content, or you want to launch with certain timing 🚀