Module-contributed sidebar.admin_nav_item slots are now rendered as
complete <details><summary> nav groups appended to the admin panel,
matching the same pattern as core groups (Organization, Roles, etc.).
Fixes undefined $moduleNavItemSlots by reading layoutNav early.
Merges mail log into the module-contributed Audit & logs group when
both exist.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>