Phase 0.2: migrate remaining SVGs to lucide-react icons

frontend/src/components/mail/MailSearchBar.tsx

@@ -5,6 +5,7 @@
 import React, { useState, useCallback } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Input } from '@/components/ui/Input';
+import { Search } from 'lucide-react';
 
 export interface MailSearchBarProps {
   onSearch: (query: string) => void;
@@ -38,9 +39,7 @@ export function MailSearchBar({ onSearch }: MailSearchBarProps) {
         className="absolute right-2 top-1/2 -translate-y-1/2 p-1.5 rounded-md hover:bg-secondary-100 min-h-touch min-w-touch"
         aria-label={t('common.search')}
       >
-        <svg className="w-4 h-4 text-secondary-400" fill="none" viewBox="0 0 24 24" stroke="currentColor" aria-hidden="true">
-          <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z" />
-        </svg>
+        <Search className="w-4 h-4 text-secondary-400" aria-hidden="true" strokeWidth={2} />
       </button>
     </form>
   );