feat: 收藏夹系统 + Studio 趋势图 + 通知偏好设置

- 新增收藏夹系统 (Folder/FolderItem 模型、CRUD API、前端管理页)
- 新增文章详情页收藏按钮 (书签图标、ToggleFavorite 一键收藏)
- 新增 Studio 趋势图 (赋能值/评论/点赞/收藏 4 线图, 7d/30d/90d)
- 新增通知偏好设置页 (评论/回复/点赞/关注 4 类开关)
- 后端通知列表支持按偏好过滤 (排除已关闭的通知类型)
- 下载 Chart.js 到本地静态资源 (static/js/chart.umd.min.js)
- 补充收藏夹卡片、开关滑块、趋势图网格等 CSS 样式

cmd/server/main.go

@@ -27,7 +27,7 @@ func main() {
 	if err != nil {
 		log.Fatalf("连接数据库失败: %v", err)
 	}
-	if err := db.AutoMigrate(&model.User{}, &model.AuditSubmission{}, &model.SiteSetting{}, &model.Notification{}, &model.Post{}, &model.UserCheckIn{}, &model.UserTask{}, &model.EnergyLog{}, &model.PostEnergizeLog{}, &model.DailyExpSummary{}, &model.Comment{}, &model.CommentMention{}, &model.CommunityFund{}, &model.FundLog{}, &model.PostLike{}, &model.PostDislike{}, &model.UserFollow{}, &model.DailyLikeSummary{}); err != nil {
+	if err := db.AutoMigrate(&model.User{}, &model.AuditSubmission{}, &model.SiteSetting{}, &model.Notification{}, &model.Post{}, &model.UserCheckIn{}, &model.UserTask{}, &model.EnergyLog{}, &model.PostEnergizeLog{}, &model.DailyExpSummary{}, &model.Comment{}, &model.CommentMention{}, &model.CommunityFund{}, &model.FundLog{}, &model.PostLike{}, &model.PostDislike{}, &model.UserFollow{}, &model.DailyLikeSummary{}, &model.Folder{}, &model.FolderItem{}); err != nil {
 		log.Fatalf("数据库迁移失败: %v", err)
 	}