Day 9 完了

実装内容:
1. backend/apps/fields/views.py - FieldViewSetをModelViewSetに変更（書き込み可能）
2. frontend/src/components/Navbar.tsx - 圃場管理リンク追加
3. frontend/src/app/fields/page.tsx - 圃場一覧画面
4. frontend/src/app/fields/new/page.tsx - 新規作成画面
5. frontend/src/app/fields/[id]/page.tsx - 編集画面
API CRUDテスト結果:
- POST /api/fields/ → 201 Created
- GET /api/fields/ → 200 OK
- PATCH /api/fields/{id}/ → 200 OK
- DELETE /api/fields/{id}/ → 204 No Content
ブラウザで http://localhost:3000/fields から圃場のCRUD操作が可能です。
次の工程に移りますか？

frontend/src/components/Navbar.tsx

@@ -1,23 +1,49 @@
 'use client';
 
-import { useRouter } from 'next/navigation';
-import { LogOut } from 'lucide-react';
+import { useRouter, usePathname } from 'next/navigation';
+import { LogOut, Wheat, MapPin } from 'lucide-react';
 import { logout } from '@/lib/api';
 
 export default function Navbar() {
   const router = useRouter();
+  const pathname = usePathname();
 
   const handleLogout = () => {
     logout();
   };
 
+  const isActive = (path: string) => pathname === path;
+
   return (
     <nav className="bg-white shadow-sm border-b border-gray-200">
       <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
         <div className="flex justify-between h-16">
-          <div className="flex items-center">
+          <div className="flex items-center space-x-8">
             <h1 className="text-xl font-bold text-green-700">KeinaSystem</h1>
-            <span className="ml-2 text-sm text-gray-500">農業管理システム</span>
+            <div className="flex items-center space-x-4">
+              <button
+                onClick={() => router.push('/allocation')}
+                className={`flex items-center px-3 py-2 text-sm rounded-md transition-colors ${
+                  isActive('/allocation')
+                    ? 'text-green-700 bg-green-50'
+                    : 'text-gray-700 hover:text-gray-900 hover:bg-gray-100'
+                }`}
+              >
+                <Wheat className="h-4 w-4 mr-2" />
+                作付け計画
+              </button>
+              <button
+                onClick={() => router.push('/fields')}
+                className={`flex items-center px-3 py-2 text-sm rounded-md transition-colors ${
+                  isActive('/fields') || pathname?.startsWith('/fields/')
+                    ? 'text-green-700 bg-green-50'
+                    : 'text-gray-700 hover:text-gray-900 hover:bg-gray-100'
+                }`}
+              >
+                <MapPin className="h-4 w-4 mr-2" />
+                圃場管理
+              </button>
+            </div>
           </div>
           <div className="flex items-center">
             <button