- add new metadata global with URL, title, description, keywords, Open Graph, Twitter, and image fields
- register Metadata global in payload.config.ts
- switch frontend layout to generateMetadata() and load metadata values from Payload globals
- resolve metadata image relation (ID or populated media) for OG/Twitter images
- update live preview globals config to use SiteSettings.slug and HomePage.slug
- keep SiteSettings revalidation hook in consistent position within config
- regenerate payload-types.ts for new global/schema types
