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/hooks/useUsers.ts

@@ -1,5 +1,5 @@
 import { useQuery } from '@tanstack/react-query';
-import { apiClient } from '../api/client';
+import apiClient from '../api/client';
 import { User } from '../types';
 
 /**