Lookup values overhaul and curator navigation

Lookup values overhaul - the admin lookups page now has per-category detail pages, icon support for values, and a cleaner management experience.

Curator navigation - prev/next buttons on all curator entity view pages for quick browsing between entries without returning to the list.

Entity link suggestions - when editing entity descriptions, the system now auto-detects references to other entities and suggests converting them to cross-reference links.

Slug redirects - renaming an entity automatically creates a 301 redirect from the old URL, so existing links and bookmarks continue to work.