Guide maintenance now tracks sources and revision notes

What changed

Guide pages now expose source references and revision notes at the page level. The goal is to make the maintenance trail visible without pretending that every article has hands-on product testing behind it.

• Default sources are assigned by article category.
• Article-specific sources can override the defaults.
• Revision notes explain material updates instead of changing dates for optics.

How this helps readers

Sleep products change often: model names shift, fiber labels get revised, and affiliate listings can default to the wrong variation. A visible source trail makes it clearer what the guide is relying on and when it was last checked.

How this helps search quality

The operating standard is people-first content: useful pages, crawlable links, transparent disclosures, and no fabricated ratings. New health checks enforce those expectations before deployment.