feat: Add comprehensive sandbox mode, public API system, and platform support

This commit adds major features for sandbox isolation, public API access, and platform support ticketing.

## Sandbox Mode
- Add sandbox mode toggle for businesses to test features without affecting live data
- Implement schema-based isolation for tenant data (appointments, resources, services)
- Add is_sandbox field filtering for shared models (customers, staff, tickets)
- Create sandbox middleware to detect and set sandbox mode from cookies
- Add sandbox context and hooks for React frontend
- Display sandbox banner when in test mode
- Auto-reload page when switching between live/test modes
- Prevent platform support tickets from being created in sandbox mode

## Public API System
- Full REST API for external integrations with businesses
- API token management with sandbox/live token separation
- Test tokens (ss_test_*) show full plaintext for easy testing
- Live tokens (ss_live_*) are hashed and secure
- Security validation prevents live token plaintext storage
- Comprehensive test suite for token security
- Rate limiting and throttling per token
- Webhook support for real-time event notifications
- Scoped permissions system (read/write per resource type)
- API documentation page with interactive examples
- Token revocation with confirmation modal

## Platform Support
- Dedicated support page for businesses to contact SmoothSchedule
- View all platform support tickets in one place
- Create new support tickets with simplified interface
- Reply to existing tickets with conversation history
- Platform tickets have no admin controls (no priority/category/assignee/status)
- Internal notes hidden for platform tickets (business can't see them)
- Quick help section with links to guides and API docs
- Sandbox warning prevents ticket creation in test mode
- Business ticketing retains full admin controls (priority, assignment, internal notes)

## UI/UX Improvements
- Add notification dropdown with real-time updates
- Staff permissions UI for ticket access control
- Help dropdown in sidebar with Platform Guide, Ticketing Help, API Docs, and Support
- Update sidebar "Contact Support" to "Support" with message icon
- Fix navigation links to use React Router instead of anchor tags
- Remove unused language translations (Japanese, Portuguese, Chinese)

## Technical Details
- Sandbox middleware sets request.sandbox_mode from cookies
- ViewSets filter data by is_sandbox field
- API authentication via custom token auth class
- WebSocket support for real-time ticket updates
- Migration for sandbox fields on User, Tenant, and Ticket models
- Comprehensive documentation in SANDBOX_MODE_IMPLEMENTATION.md

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

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

frontend/src/layouts/PlatformLayout.tsx

@@ -1,9 +1,12 @@
 import React, { useState } from 'react';
 import { Outlet } from 'react-router-dom';
-import { Moon, Sun, Bell, Globe, Menu } from 'lucide-react';
+import { Moon, Sun, Globe, Menu } from 'lucide-react';
 import { User } from '../types';
 import PlatformSidebar from '../components/PlatformSidebar';
 import UserProfileDropdown from '../components/UserProfileDropdown';
+import NotificationDropdown from '../components/NotificationDropdown';
+import TicketModal from '../components/TicketModal';
+import { useTicket } from '../hooks/useTickets';
 import { useScrollToTop } from '../hooks/useScrollToTop';
 
 interface PlatformLayoutProps {
@@ -16,9 +19,21 @@ interface PlatformLayoutProps {
 const PlatformLayout: React.FC<PlatformLayoutProps> = ({ user, darkMode, toggleTheme, onSignOut }) => {
   const [isCollapsed, setIsCollapsed] = useState(false);
   const [isMobileMenuOpen, setIsMobileMenuOpen] = useState(false);
+  const [ticketModalId, setTicketModalId] = useState<string | null>(null);
 
   useScrollToTop();
 
+  // Fetch ticket data when modal is opened from notification
+  const { data: ticketFromNotification } = useTicket(ticketModalId || undefined);
+
+  const handleTicketClick = (ticketId: string) => {
+    setTicketModalId(ticketId);
+  };
+
+  const closeTicketModal = () => {
+    setTicketModalId(null);
+  };
+
   return (
     <div className="flex h-screen bg-gray-100 dark:bg-gray-900">
       {/* Mobile menu */}
@@ -59,9 +74,7 @@ const PlatformLayout: React.FC<PlatformLayoutProps> = ({ user, darkMode, toggleT
                 >
                     {darkMode ? <Sun size={20} /> : <Moon size={20} />}
                 </button>
-                <button className="p-2 text-gray-400 hover:text-gray-600 dark:hover:text-gray-200 transition-colors">
-                    <Bell size={20} />
-                </button>
+                <NotificationDropdown onTicketClick={handleTicketClick} />
                 <UserProfileDropdown user={user} />
             </div>
         </header>
@@ -70,6 +83,14 @@ const PlatformLayout: React.FC<PlatformLayoutProps> = ({ user, darkMode, toggleT
           <Outlet />
         </main>
       </div>
+
+      {/* Ticket modal opened from notification */}
+      {ticketModalId && ticketFromNotification && (
+        <TicketModal
+          ticket={ticketFromNotification}
+          onClose={closeTicketModal}
+        />
+      )}
     </div>
   );
 };