feat(notification): 通知标题和正文支持多语言

- 通知静态配置支持 title/body i18n
- 前端通知列表和详情页展示本地化内容
- 新增数据库迁移脚本
- 更新通知协议文档

apps/lib/shared/widgets/notification/notification_detail_bottom_sheet.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 
 import '../../../features/notifications/data/models/notification_item.dart';
 import '../../theme/design_tokens.dart';
+import '../../utils/time_format.dart';
 
 class NotificationDetailBottomSheet extends StatefulWidget {
   const NotificationDetailBottomSheet({
@@ -76,7 +77,7 @@ class _NotificationDetailBottomSheetState
           Padding(
             padding: const EdgeInsets.symmetric(horizontal: AppSpacing.lg),
             child: Text(
-              _formatTime(widget.item.createdAt),
+              formatRelativeTime(context, widget.item.createdAt),
               style: textTheme.labelSmall?.copyWith(color: colors.outline),
             ),
           ),
@@ -97,16 +98,6 @@ class _NotificationDetailBottomSheetState
       ),
     );
   }
-
-  String _formatTime(DateTime dt) {
-    final now = DateTime.now();
-    final diff = now.difference(dt);
-    if (diff.inMinutes < 1) return '刚刚';
-    if (diff.inHours < 1) return '${diff.inMinutes}分钟前';
-    if (diff.inDays < 1) return '${diff.inHours}小时前';
-    if (diff.inDays < 30) return '${diff.inDays}天前';
-    return '${dt.month}/${dt.day}';
-  }
 }
 
 Future<void> showNotificationDetailBottomSheet({