fix(*): 公告与画布 - 支持公告重新发布并阻止浏览器误缩放

Fixes #55

backend/internal/repository/announcement.go

@@ -60,6 +60,28 @@ func (r *Repository) CloseAnnouncement(id string, closedAt time.Time) (bool, err
 	return result.RowsAffected == 1, result.Error
 }
 
+func (r *Repository) UpdateAnnouncement(announcement *model.Announcement) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		result := tx.Model(&model.Announcement{}).Where("id = ?", announcement.ID).Updates(map[string]any{
+			"title":        announcement.Title,
+			"content":      announcement.Content,
+			"level":        announcement.Level,
+			"status":       announcement.Status,
+			"published_at": announcement.PublishedAt,
+			"closed_at":    announcement.ClosedAt,
+			"updated_at":   announcement.UpdatedAt,
+		})
+		if result.Error != nil {
+			return result.Error
+		}
+		if result.RowsAffected != 1 {
+			return gorm.ErrRecordNotFound
+		}
+		// 重新发布同一公告必须清除旧已读记录，否则用户看不到新的内容提醒。
+		return tx.Where("announcement_id = ?", announcement.ID).Delete(&model.UserAnnouncementRead{}).Error
+	})
+}
+
 func (r *Repository) MarkAnnouncementsRead(userID string, announcementIDs []string, readAt time.Time) error {
 	if len(announcementIDs) == 0 {
 		return nil