feat: Implement unified sidebar with Nuxt UI across all dashboard pages

- Install @nuxt/ui and integrate with existing Vuetify
- Create new layouts/dashboard-unified.vue with modern sidebar design
- Features: clean white design, collapsible sidebar, role-based navigation
- Remove old layouts/dashboard.vue to eliminate dual-sidebar confusion
- Update all dashboard pages to use dashboard-unified layout
- Add demo page showcasing new sidebar features
- Fix auth error handler to ignore external service 401 errors
- Ensure consistent navigation experience across entire platform

pages/dashboard/admin/audit-logs.vue

@@ -238,6 +238,7 @@ import { formatDate, formatTime, formatDateTime } from '@/utils/dateUtils'
 
 definePageMeta({
   middleware: ['authentication', 'authorization'],
+  layout: 'dashboard-unified',
   auth: {
     roles: ['admin']
   }

pages/dashboard/admin/system-logs.vue

@@ -230,6 +230,7 @@ import { formatTime, formatDateTime } from '@/utils/dateUtils'
 
 definePageMeta({
   middleware: ['authentication', 'authorization'],
+  layout: 'dashboard-unified',
   auth: {
     roles: ['admin']
   }