feat: Implement staff invitation system with role-based permissions

- Add StaffInvitation model with token-based 7-day expiration
- Create invitation API endpoints (create, cancel, resend, accept, decline)
- Add permissions JSONField to User model for granular access control
- Implement frontend invite modal with role-specific permissions:
  - Manager: can_invite_staff, can_manage_resources, can_manage_services,
    can_view_reports, can_access_settings, can_refund_payments
  - Staff: can_view_all_schedules, can_manage_own_appointments
- Add edit staff modal with permissions management and deactivate option
- Create AcceptInvitePage for invitation acceptance flow
- Add active/inactive staff separation with collapsible section
- Auto-create bookable resource when configured at invite time
- Remove Quick Add Appointment from dashboard

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/pages/Dashboard.tsx

@@ -16,7 +16,6 @@ import { useServices } from '../hooks/useServices';
 import { useResources } from '../hooks/useResources';
 import { useAppointments } from '../hooks/useAppointments';
 import { useCustomers } from '../hooks/useCustomers';
-import QuickAddAppointment from '../components/QuickAddAppointment';
 
 interface Metric {
   label: string;
@@ -147,14 +146,9 @@ const Dashboard: React.FC = () => {
         ))}
       </div>
 
-      <div className="grid grid-cols-1 gap-6 lg:grid-cols-3">
-        {/* Quick Add Appointment */}
-        <div className="lg:col-span-1">
-          <QuickAddAppointment />
-        </div>
-
+      <div className="grid grid-cols-1 gap-6">
         {/* Revenue Chart */}
-        <div className="lg:col-span-2 p-6 bg-white dark:bg-gray-800 border border-gray-100 dark:border-gray-700 rounded-xl shadow-sm transition-colors duration-200">
+        <div className="p-6 bg-white dark:bg-gray-800 border border-gray-100 dark:border-gray-700 rounded-xl shadow-sm transition-colors duration-200">
           <h3 className="mb-6 text-lg font-semibold text-gray-900 dark:text-white">{t('dashboard.totalRevenue')}</h3>
           <div className="h-80">
             <ResponsiveContainer width="100%" height="100%">