Phase 0.2: migrate remaining SVGs to lucide-react icons

frontend/src/components/calendar/CalendarTree.tsx

@@ -10,6 +10,7 @@ import React, { useState } from 'react';
 import clsx from 'clsx';
 import { useTranslation } from 'react-i18next';
 import type { Calendar, CalendarType } from '@/api/calendar';
+import { ChevronDown, Plus } from 'lucide-react';
 
 const TYPE_ORDER: CalendarType[] = ['personal', 'team', 'project', 'company'];
 
@@ -115,9 +116,7 @@ function TypeSection({
           className="flex-shrink-0 w-4 h-4 flex items-center justify-center text-secondary-400 hover:text-secondary-600"
           aria-label={expanded ? 'Collapse' : 'Expand'}
         >
-          <svg className="w-3 h-3 transition-transform" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
-            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d={expanded ? 'M19 9l-7 7-7-7' : 'M9 5l7 7-7 7'} />
-          </svg>
+          <ChevronDown className="w-3 h-3 transition-transform" aria-hidden="true" strokeWidth={2} />
         </button>
         <span className="truncate text-secondary-700">{t(`calendar.type.${type}`)}</span>
         <span className="ml-auto text-xs text-secondary-400">{calendars.length}</span>
@@ -218,9 +217,7 @@ export function CalendarTree({
           )}
           data-testid="calendar-tree-new"
         >
-          <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
-            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M12 4v16m8-8H4" />
-          </svg>
+          <Plus className="w-4 h-4" aria-hidden="true" strokeWidth={2} />
           {t('calendar.tree.newCalendar')}
         </button>
       </div>