Phase 0.2: migrate remaining SVGs to lucide-react icons

frontend/src/components/mail/TemplatePicker.tsx

@@ -8,6 +8,8 @@ import { useTranslation } from 'react-i18next';
 import { fetchTemplates, substituteTemplate, type MailTemplate } from '@/api/mail';
 import { EmptyState } from '@/components/ui/EmptyState';
 
+import { Loader2 } from 'lucide-react';
+
 export interface TemplatePickerProps {
   onSelect: (body: string, subject: string) => void;
 }
@@ -55,10 +57,7 @@ export function TemplatePicker({ onSelect }: TemplatePickerProps) {
   if (loading) {
     return (
       <div className="flex items-center justify-center py-4" data-testid="template-picker-loading">
-        <svg className="animate-spin h-5 w-5 text-secondary-400" fill="none" viewBox="0 0 24 24" aria-hidden="true">
-          <circle className="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" strokeWidth="4" />
-          <path className="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z" />
-        </svg>
+        <Loader2 className="animate-spin h-5 w-5 text-secondary-400" aria-hidden="true" />
         <span className="ml-2 text-sm text-secondary-500">{t('common.loading')}</span>
       </div>
     );