Phase 0.2: migrate remaining SVGs to lucide-react icons

frontend/src/components/mail/PgpSettings.tsx

@@ -9,6 +9,8 @@ import { Input } from '@/components/ui/Input';
 import { Card } from '@/components/ui/Card';
 import { EmptyState } from '@/components/ui/EmptyState';
 import { useToast } from '@/components/ui/Toast';
+
+import { Loader2 } from 'lucide-react';
 import {
   importPgpKey,
   fetchPgpKeys,
@@ -83,10 +85,7 @@ export function PgpSettings() {
   if (loading) {
     return (
       <div className="flex items-center justify-center py-8" data-testid="pgp-settings-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" />
       </div>
     );
   }