feat(ui): open list items counter on Listen, none on Workspace

New stat listItemsOpenCount: unchecked items in all lists the user sees
(own, shared directly or through a group), shown as accent counter on
Listen in the header and the mobile bottom bar. Workspace loses its
counter. Stats refresh on list events and after deleting an item.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/domain/models.go

@@ -520,6 +520,7 @@ type DashboardStats struct {
 	DocsCount          int `json:"docsCount"`
 	DocsTodosOpenCount int `json:"docsTodosOpenCount"`
 	ListsCount         int `json:"listsCount"`
+	ListItemsOpenCount int `json:"listItemsOpenCount"` // unchecked items in all lists the user sees
 	DiscardedCount     int `json:"discardedCount"`
 }