散布実績ページ: useSearchParamsをSuspense boundaryでラップ（本番ビルドエラー修正）

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/app/fertilizer/spreading/page.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useEffect, useMemo, useState } from 'react';
+import { Suspense, useEffect, useMemo, useState } from 'react';
 import { useRouter, useSearchParams } from 'next/navigation';
 import { ChevronLeft, Pencil, Plus, Save, Sprout, Trash2, X } from 'lucide-react';
 
@@ -89,6 +89,14 @@ const buildCreateInitialValues = (rows: SpreadingCandidate[], sourceType: Source
 };
 
 export default function SpreadingPage() {
+  return (
+    <Suspense fallback={<div className="min-h-screen bg-gray-50"><Navbar /><div className="max-w-7xl mx-auto px-4 py-8 text-gray-500">読み込み中...</div></div>}>
+      <SpreadingPageContent />
+    </Suspense>
+  );
+}
+
+function SpreadingPageContent() {
   const router = useRouter();
   const searchParams = useSearchParams();
   const queryYear = Number(searchParams.get('year') || '0') || null;