feat(announcement): 新增首页弹窗公告功能并完成弹窗UI视觉重构

- 数据库与后端：announcements 表增加 is_popup 字段及迁移脚本，提供前台弹窗接口与多公告优先级选取，补全选优单测
- 管理后台：总后台与分销后台公告编辑新增「弹窗公告」开关与列表标签展示
- 前台交互：前台 PC/移动端首页引入 AnnouncementPopup，支持同一用户同一天同一公告仅弹一次的关闭记录
- 视觉优化：重构弹窗结构，顶栏镶嵌品牌橙流光细条与浅暖橙通知徽标，中间内嵌浅灰舒适阅读卡片，底部搭配大锤橙实心主操作按钮
- 验证方式：后端 announcement 单测通过，前端 npm run build 编译无报错，浏览器实机截图验证

backend/internal/modules/distribution/announcement.go

@@ -90,6 +90,7 @@ func (r *Repository) CreateSiteAnnouncement(ctx context.Context, adminID, siteID
 		Priority:           req.Priority,
 		IsPinned:           req.IsPinned,
 		IsImportant:        req.IsImportant,
+		IsPopup:            req.IsPopup,
 		Status:             "draft",
 		CreatedBy:          &createdBy,
 	}
@@ -120,6 +121,7 @@ func (r *Repository) UpdateSiteAnnouncement(ctx context.Context, adminID, siteID
 		"priority":     req.Priority,
 		"is_pinned":    req.IsPinned,
 		"is_important": req.IsImportant,
+		"is_popup":     req.IsPopup,
 	}
 	if title := strings.TrimSpace(req.Title); title != "" {
 		updates["title"] = title
@@ -217,6 +219,7 @@ func toSiteAnnouncementDTO(a model.Announcement) SiteAnnouncementDTO {
 		Priority:           a.Priority,
 		IsPinned:           a.IsPinned,
 		IsImportant:        a.IsImportant,
+		IsPopup:            a.IsPopup,
 		ViewCount:          a.ViewCount,
 		Status:             a.Status,
 		PublishedAt:        a.PublishedAt,

backend/internal/modules/distribution/dto.go

@@ -449,6 +449,7 @@ type SiteAnnouncementDTO struct {
 	Priority           int        `json:"priority"`
 	IsPinned           bool       `json:"is_pinned"`
 	IsImportant        bool       `json:"is_important"`
+	IsPopup            bool       `json:"is_popup"`
 	ViewCount          int        `json:"view_count"`
 	Status             string     `json:"status"`
 	PublishedAt        *time.Time `json:"published_at"`
@@ -470,6 +471,8 @@ type CreateSiteAnnouncementRequest struct {
 	Priority    int    `json:"priority"`
 	IsPinned    bool   `json:"is_pinned"`
 	IsImportant bool   `json:"is_important"`
+	// IsPopup 弹窗公告：本站首页弹出且需用户手动关闭，同一天只弹一次。
+	IsPopup bool `json:"is_popup"`
 }
 
 type UpdateSiteAnnouncementRequest struct {
@@ -479,6 +482,7 @@ type UpdateSiteAnnouncementRequest struct {
 	Priority    int    `json:"priority"`
 	IsPinned    bool   `json:"is_pinned"`
 	IsImportant bool   `json:"is_important"`
+	IsPopup     bool   `json:"is_popup"`
 }
 
 // 自主加价 DTO：增加该站「1 元兑换哈夫币」比例，不是人民币。