feat(tickets): add /tickets route and sidebar nav item

Add Tickets page route to router with lazy loading and code splitting.
Add Tickets navigation entry to sidebar in RESOLVE section for both
icon rail and pinned layouts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -5,7 +5,7 @@ import {
   LayoutGrid, Clock, AlertTriangle, GitBranch, Code2, Wand2,
   ListChecks, Download, BarChart3,
   Settings, Pin, PinOff,
-  History, FileText, Network,
+  History, FileText, Network, Ticket,
 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { useUserPreferencesStore } from '@/store/userPreferencesStore'
@@ -83,6 +83,10 @@ export function Sidebar() {
         { href: '/escalations', label: 'Escalations', count: stats?.escalation_count || undefined },
       ],
     },
+    {
+      href: '/tickets', icon: Ticket, label: 'Tickets', shortLabel: 'Tickets',
+      matchPaths: ['/tickets'],
+    },
     {
       href: '/trees', icon: GitBranch, label: 'Flows', shortLabel: 'Flows',
       badge: stats?.tree_counts.total || undefined,
@@ -120,6 +124,7 @@ export function Sidebar() {
       items: [
         { href: '/', icon: LayoutGrid, label: 'Dashboard', shortLabel: 'Dash' },
         { href: '/sessions', icon: Clock, label: 'Session History', shortLabel: 'History', badge: stats?.active_count || undefined, matchPaths: ['/sessions'] },
+        { href: '/tickets', icon: Ticket, label: 'Tickets', shortLabel: 'Tickets', matchPaths: ['/tickets'] },
         { href: '/escalations', icon: AlertTriangle, label: 'Escalations', shortLabel: 'Escal', badge: stats?.escalation_count || undefined },
       ],
     },