Introduce generic explorer.nav_item slot type in app-main-aside.phtml
so modules can contribute links to the explorer nav panel.
Switch addressbook module from aside.tab_panel to explorer.nav_item.
Remove aside department-filter panel, AddressBookLayoutProvider, and
AddressBookSessionProvider (only served the now-removed aside panel).
Fix grid Name column overflow into Email column: CSS selector
.grid-name-cell > span:last-child never matched the <a> name link;
changed to :last-child and scoped flex-shrink:0 to :first-child only.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
