Nested routes, groups, and slug-based URLs

Nested routes - navigate between entities in context. View a series' books, characters, and groups from within the universe or series page. Breadcrumbs show the full navigation path.

Group detail pages - groups (factions, organisations, crews) now have their own detail pages showing members and context.

Slug-based URLs - all entities now use human-readable URLs (e.g. /series/mistborn-era-1) instead of IDs. Slugs are auto-generated and unique.

Characters and groups listings - dedicated browsing pages for characters and groups with filtering.

Fixed header and breadcrumbs - the header and breadcrumbs now stay fixed at the top of the page as you scroll.