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

internal/service/trends_service.go

@@ -0,0 +1,59 @@
+package service
+
+import "fmt"
+
+// TrendResult 趋势返回结构
+type TrendResult struct {
+	Energy    []TrendPoint `json:"energy"`
+	Comments  []TrendPoint `json:"comments"`
+	Likes     []TrendPoint `json:"likes"`
+	Favorites []TrendPoint `json:"favorites"`
+}
+
+// TrendsService Studio 趋势分析服务
+type TrendsService struct {
+	energyRepo    EnergyTrendStore
+	commentRepo   CommentTrendStore
+	likeRepo      LikeTrendStore
+	favoriteRepo  FavoriteTrendStore
+}
+
+// NewTrendsService 构造函数
+func NewTrendsService(energyRepo EnergyTrendStore, commentRepo CommentTrendStore, likeRepo LikeTrendStore, favoriteRepo FavoriteTrendStore) *TrendsService {
+	return &TrendsService{
+		energyRepo:   energyRepo,
+		commentRepo:  commentRepo,
+		likeRepo:     likeRepo,
+		favoriteRepo: favoriteRepo,
+	}
+}
+
+// GetTrends 获取指定时间范围的趋势数据
+func (s *TrendsService) GetTrends(userID uint, since string) (*TrendResult, error) {
+	energy, err := s.energyRepo.AggregateEnergyByAuthor(userID, since)
+	if err != nil {
+		return nil, fmt.Errorf("查询赋能趋势: %w", err)
+	}
+
+	comments, err := s.commentRepo.AggregateCommentsByAuthor(userID, since)
+	if err != nil {
+		return nil, fmt.Errorf("查询评论趋势: %w", err)
+	}
+
+	likes, err := s.likeRepo.AggregateLikesByAuthor(userID, since)
+	if err != nil {
+		return nil, fmt.Errorf("查询点赞趋势: %w", err)
+	}
+
+	favorites, err := s.favoriteRepo.AggregateFavoritesByAuthor(userID, since)
+	if err != nil {
+		return nil, fmt.Errorf("查询收藏趋势: %w", err)
+	}
+
+	return &TrendResult{
+		Energy:    energy,
+		Comments:  comments,
+		Likes:     likes,
+		Favorites: favorites,
+	}, nil
+}