Add staff email client with WebSocket real-time updates

Implements a complete email client for platform staff members:

Backend:
- Add routing_mode field to PlatformEmailAddress (PLATFORM/STAFF)
- Create staff_email app with models for folders, emails, attachments, labels
- IMAP service for fetching emails with folder mapping
- SMTP service for sending emails with attachment support
- Celery tasks for periodic sync and full sync operations
- WebSocket consumer for real-time notifications
- Comprehensive API viewsets with filtering and actions

Frontend:
- Thunderbird-style three-pane email interface
- Multi-account support with drag-and-drop ordering
- Email composer with rich text editor
- Email viewer with thread support
- Real-time WebSocket updates for new emails and sync status
- 94 unit tests covering models, serializers, views, services, and consumers

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/TopBar.tsx

@@ -6,6 +6,7 @@ import UserProfileDropdown from './UserProfileDropdown';
 import LanguageSelector from './LanguageSelector';
 import NotificationDropdown from './NotificationDropdown';
 import SandboxToggle from './SandboxToggle';
+import HelpButton from './HelpButton';
 import { useSandbox } from '../contexts/SandboxContext';
 
 interface TopBarProps {
@@ -62,6 +63,8 @@ const TopBar: React.FC<TopBarProps> = ({ user, isDarkMode, toggleTheme, onMenuCl
 
         <NotificationDropdown onTicketClick={onTicketClick} />
 
+        <HelpButton />
+
         <UserProfileDropdown user={user} />
       </div>
     </header>