feat: Add SMTP settings and collapsible email configuration UI

- Add SMTP fields to TicketEmailSettings model (host, port, TLS/SSL, credentials, from email/name)
- Update serializers with SMTP fields and is_smtp_configured flag
- Add TicketEmailTestSmtpView for testing SMTP connections
- Update frontend API types and hooks for SMTP settings
- Add collapsible IMAP and SMTP configuration sections with "Configured" badges
- Fix TypeScript errors in mockData.ts (missing required fields, type mismatches)

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

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

frontend/src/components/Sidebar.tsx

@@ -22,7 +22,8 @@ import {
   Plug,
   Package,
   Clock,
-  Store
+  Store,
+  Mail
 } from 'lucide-react';
 import { Business, User } from '../types';
 import { useLogout } from '../hooks/useAuth';
@@ -226,6 +227,14 @@ const Sidebar: React.FC<SidebarProps> = ({ business, user, isCollapsed, toggleCo
                     <Package size={16} className="shrink-0" />
                     <span>{t('nav.myPlugins', 'My Plugins')}</span>
                   </Link>
+                  <Link
+                    to="/email-templates"
+                    className={`flex items-center gap-3 py-2 text-sm font-medium rounded-lg transition-colors px-3 ${location.pathname === '/email-templates' ? 'bg-white/10 text-white' : 'text-white/60 hover:text-white hover:bg-white/5'}`}
+                    title={t('nav.emailTemplates', 'Email Templates')}
+                  >
+                    <Mail size={16} className="shrink-0" />
+                    <span>{t('nav.emailTemplates', 'Email Templates')}</span>
+                  </Link>
                   <Link
                     to="/help/plugins"
                     className={`flex items-center gap-3 py-2 text-sm font-medium rounded-lg transition-colors px-3 ${location.pathname === '/help/plugins' ? 'bg-white/10 text-white' : 'text-white/60 hover:text-white hover:bg-white/5'}`}