This commit enhances the OPDS server with two major features:
1. Series Metadata in OPDS Feed:
- Add series name and book number to OPDS book entries
- Uses standard OPDS/EPUB 3 metadata format with <meta> tags
- Includes belongs-to-collection and group-position properties
2. Authors Navigation Hierarchy:
- Add new /authors endpoint for browsing books by author
- Implement authors list navigation feed with alphabetical sorting
- Add author filtering to catalog feed via ?author parameter
- Support library-based access control for author lists
- Add authors link to root OPDS navigation
Changes:
- OpdsFeedService: Add series metadata to appendMetadata(), add generateAuthorsNavigation()
- OpdsController: Add getAuthorsNavigation() endpoint
- OpdsBookService: Add getDistinctAuthors() and getBooksByAuthorName() methods
- BookOpdsRepository: Add queries for distinct authors and books by author name
- Updated generateCatalogFeed() to support author parameter
- Updated determineFeedTitle() and determineFeedId() to handle author context