fix: restore removed icon imports in MyTreesPage, add default export to SessionHistoryPage

- FolderTree, Plus, ListOrdered, Wrench are still used in empty state
  and tree card rendering — restore the imports
- SessionHistoryPage needs default export for lazyWithRetry

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/MyTreesPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from 'react'
 import { useNavigate, Link } from 'react-router-dom'
-import { Play, Pencil, Share2, Trash2, GitBranch, Clock, TrendingUp } from 'lucide-react'
+import { Play, Pencil, Share2, Trash2, GitBranch, Clock, TrendingUp, FolderTree, Plus, ListOrdered, Wrench } from 'lucide-react'
 import { PageMeta } from '@/components/common/PageMeta'
 import { StaggerList } from '@/components/common/StaggerList'
 import { Button } from '@/components/ui/Button'

frontend/src/pages/SessionHistoryPage.tsx

@@ -26,7 +26,7 @@ const TABS = [
 
 type TabId = typeof TABS[number]['id']
 
-export function SessionHistoryPage() {
+export default function SessionHistoryPage() {
   const navigate = useNavigate()
   const [searchParams, setSearchParams] = useSearchParams()
   const [activeTab, setActiveTab] = useState<TabId>('ai')