Delete old Vuexy VerticalNav layout system (5 components + 4 SCSS files)
and replace with new modular components: AppSidebar, AppTopNavbar,
CommandPalette, NotificationPanel, ToastStack, SkeletonLoader,
EmptyState, Breadcrumbs. Rebuild all 4 layouts (Admin, Account,
Marketing, Auth) using new components. Add Pinia toast store for
flash message integration. Update navigation with cleaner groupings.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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