feat: Redesign navigation menu like Close.com

- Inbox, Chancen (Pipeline), Leads, Kontakte, Firmen, Aktivitäten
- Konversationen, Workflows, Berichte (coming soon)
- Team & Einstellungen at bottom
- Expandable submenus for Leads and Workflows
- User profile at top of sidebar
- German labels

src/router/index.js

@@ -23,6 +23,11 @@ const routes = [
         name: 'Inbox',
         component: () => import('@/views/InboxView.vue')
       },
+      {
+        path: 'leads',
+        name: 'Leads',
+        component: () => import('@/views/ContactsView.vue') // Uses contacts view for now
+      },
       {
         path: 'contacts',
         name: 'Contacts',