feat: 記録日時を一覧カードと詳細画面に表示

- sake_list_item: カード末尾に相対日付を追加
  今日 / 昨日 / N日前 / M/D / YYYY/M/D
- sake_basic_info_section: 蔵元行直下にカレンダーアイコン + 「YYYY年M月D日に記録」を追加
  セット商品は非表示
- metadata.createdAt（非null保証）を使用、追加フィールド不要

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

lib/screens/sake_detail/sections/sake_basic_info_section.dart

@@ -8,6 +8,10 @@ import '../../../constants/app_constants.dart';
 import '../../../providers/theme_provider.dart';
 import '../../../services/mbti_compatibility_service.dart';
 
+String _formatRecordedDate(DateTime date) {
+  return '${date.year}年${date.month}月${date.day}日に記録';
+}
+
 /// 銘柄名・蔵元/都道府県・タグ・AI確信度バッジ・MBTI相性バッジ・キャッチコピーを表示するセクション
 class SakeBasicInfoSection extends ConsumerWidget {
   final SakeItem sake;
@@ -161,6 +165,24 @@ class SakeBasicInfoSection extends ConsumerWidget {
               ),
             ),
           ),
+        const SizedBox(height: 8),
+
+        // 記録日
+        if (sake.itemType != ItemType.set)
+          Center(
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Icon(LucideIcons.calendarDays, size: 11, color: appColors.textTertiary),
+                const SizedBox(width: 4),
+                Text(
+                  _formatRecordedDate(sake.metadata.createdAt),
+                  style: TextStyle(fontSize: 11, color: appColors.textTertiary),
+                ),
+              ],
+            ),
+          ),
+
         const SizedBox(height: 20),
 
         // キャッチコピー（位置を銘柄名直下に移動して存在感を強調）

lib/widgets/home/sake_list_item.dart

@@ -188,6 +188,8 @@ class SakeListItem extends ConsumerWidget {
                     if (!isMenuMode && sake.itemType != ItemType.set) ...[
                       const SizedBox(height: 6),
                       _buildSpecLine(context, appColors),
+                      const SizedBox(height: 4),
+                      _buildRecordedDate(appColors),
                     ],
                   ],
                 ),
@@ -200,6 +202,36 @@ class SakeListItem extends ConsumerWidget {
     );       // Pressable
   }
 
+  /// 記録日（相対表示）
+  Widget _buildRecordedDate(AppColors appColors) {
+    final date = sake.metadata.createdAt;
+    final now = DateTime.now();
+    final today = DateTime(now.year, now.month, now.day);
+    final itemDay = DateTime(date.year, date.month, date.day);
+    final diff = today.difference(itemDay).inDays;
+
+    final String label;
+    if (diff == 0) {
+      label = '今日';
+    } else if (diff == 1) {
+      label = '昨日';
+    } else if (diff < 7) {
+      label = '$diff日前';
+    } else if (date.year == now.year) {
+      label = '${date.month}/${date.day}';
+    } else {
+      label = '${date.year}/${date.month}/${date.day}';
+    }
+
+    return Text(
+      label,
+      style: TextStyle(
+        fontSize: 10,
+        color: appColors.textTertiary,
+      ),
+    );
+  }
+
   /// 特定名称 + アルコール度数（どちらもある場合は両方、片方のみも対応）
   Widget _buildSpecLine(BuildContext context, AppColors appColors) {
     final type = sake.hiddenSpecs.type;