refactor: quality and consolidation cleanup

[woerndl]

Behavior-preserving cleanup pass.

• Extract a shared publishedRelationField factory for the posts/authors list blocks; hoist the autosave interval to a named constant.
• Reuse the shared isLocale guard in the web pickLocale.
• Derive Payload's defaultLocale from the shared constant and assert at boot that the CMS locale set matches it.
• Funnel the seed's data casts through one seedData helper.
• Collapse the triggerDeploy hook bodies behind a single post() helper; route Img/PreviewToolbar/sdk URL building through the existing absoluteCmsURL.
• Make the JSON-LD pages branch an explicit narrowing; mark the dev-only path refetch.