feat: expand Harbor eBook library and reader

[capex122]

Summary

• add the complete eBook home, discovery, collections, metadata, source setup, and plugin experience
• add Harbor and book reader modes with annotations, custom fonts, cached translation, narration, line tracking, and reading controls
• add EPUB/local-folder support, offline export, downloads integration, smart caching, and incremental loading
• add metadata-driven adaptations, recommendations, awards, collections, browsing filters, and language support
• refine sidebar navigation, eBook context menus, external links, and source/plugin documentation

Validation

• TypeScript typecheck passed
• capability JSON and git diff checks passed
• focused regression tests are included for eBook filters, caching, collections, narration, plugin guidance, source metadata, and wheel menus