feat: Enhance ticketing system with categories, templates, SLA tracking, and fix frontend integration

- Add ticket categories (billing, technical, feature_request, etc.) with type-specific options
- Add TicketTemplate and CannedResponse models for quick ticket creation
- Implement SLA tracking with due_at and first_response_at fields
- Add is_platform_admin and is_customer helper functions to fix permission checks
- Register models in Django admin with filters and fieldsets
- Enhance signals with error handling for WebSocket notifications
- Fix frontend API URLs for templates and canned responses
- Update PlatformSupport page to use real ticketing API
- Add comprehensive i18n translations for all ticket fields

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

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

frontend/src/components/Sidebar.tsx

@@ -10,7 +10,8 @@ import {
   MessageSquare,
   LogOut,
   ClipboardList,
-  Briefcase
+  Briefcase,
+  Ticket
 } from 'lucide-react';
 import { Business, User } from '../types';
 import { useLogout } from '../hooks/useAuth';
@@ -135,7 +136,7 @@ const Sidebar: React.FC<SidebarProps> = ({ business, user, isCollapsed, toggleCo
               {!isCollapsed && <span>{t('nav.resources')}</span>}
             </Link>
             <Link to="/tickets" className={getNavClass('/tickets')} title={t('nav.tickets')}>
-              <LayoutDashboard size={20} className="shrink-0" /> {/* Using LayoutDashboard icon for now, can change */}
+              <Ticket size={20} className="shrink-0" />
               {!isCollapsed && <span>{t('nav.tickets')}</span>}
             </Link>
           </>