Multi-author support, book synopses, and content requests

Multi-author support - books and series can now have multiple authors with roles (author, illustrator, editor, etc.). Author names are shown with role labels on detail pages.

Book synopses - book descriptions are now pulled from Open Library with proper attribution and database caching.

Content request workflow - simplified 8-status model with validation, voting improvements, and curator workflow actions.

Author images - author photos and bios are automatically fetched from Open Library when creating new authors.

SEO improvements - entity types in page titles (e.g. "Kelsier (Character)"), cross-entity link fixes, and loading skeletons for 13 nested routes.