Add rice transplant planning feature

frontend/src/components/Navbar.tsx

@@ -1,7 +1,7 @@
 'use client';
 
 import { useRouter, usePathname } from 'next/navigation';
-import { LogOut, Wheat, MapPin, FileText, Upload, LayoutDashboard, History, Shield, KeyRound, Cloud, Sprout, FlaskConical, Package, NotebookText, PencilLine, Construction } from 'lucide-react';
+import { LogOut, Wheat, MapPin, FileText, Upload, LayoutDashboard, History, Shield, KeyRound, Cloud, Sprout, FlaskConical, Package, NotebookText, PencilLine, Construction, Tractor } from 'lucide-react';
 import { logout } from '@/lib/api';
 
 export default function Navbar() {
@@ -122,6 +122,17 @@ export default function Navbar() {
                 <Sprout className="h-4 w-4 mr-2" />
                 施肥計画
               </button>
+              <button
+                onClick={() => router.push('/rice-transplant')}
+                className={`flex items-center px-3 py-2 text-sm rounded-md transition-colors ${
+                  pathname?.startsWith('/rice-transplant')
+                    ? 'text-green-700 bg-green-50'
+                    : 'text-gray-700 hover:text-gray-900 hover:bg-gray-100'
+                }`}
+              >
+                <Tractor className="h-4 w-4 mr-2" />
+                田植え計画
+              </button>
               <button
                 onClick={() => router.push('/fertilizer/spreading')}
                 className={`flex items-center px-3 py-2 text-sm rounded-md transition-colors ${