refactor: replace standard log with zap logger and optimize code patterns

- Migrate all log.Printf/log.Println calls to structured zap logging
- Use cmp.Or for cleaner default value handling
- Replace manual loops with slices.ContainsFunc/IndexFunc
- Add batch query methods (IsLikedBatch, IsFavoritedBatch) to solve N+1 problem
- Update JSON tags from omitempty to omitzero for numeric fields
- Use errgroup-style wg.Go for worker goroutines
- Remove duplicate casbin/v2 dependency (keeping v3)
- Add plans/ to gitignore

internal/repository/post_repo.go

@@ -285,6 +285,33 @@ func (r *PostRepository) IsLiked(postID, userID string) bool {
 	return count > 0
 }
 
+// IsLikedBatch 批量检查是否点赞（解决 N+1 问题）
+// 返回 map[postID]bool
+func (r *PostRepository) IsLikedBatch(postIDs []string, userID string) map[string]bool {
+	result := make(map[string]bool)
+	if len(postIDs) == 0 || userID == "" {
+		return result
+	}
+
+	// 初始化所有 postID 为 false
+	for _, postID := range postIDs {
+		result[postID] = false
+	}
+
+	// 一次性查询所有点赞记录
+	var likedPostIDs []string
+	r.db.Model(&model.PostLike{}).
+		Where("post_id IN ? AND user_id = ?", postIDs, userID).
+		Pluck("post_id", &likedPostIDs)
+
+	// 更新已点赞的帖子
+	for _, postID := range likedPostIDs {
+		result[postID] = true
+	}
+
+	return result
+}
+
 // Favorite 收藏帖子
 func (r *PostRepository) Favorite(postID, userID string) error {
 	return r.db.Transaction(func(tx *gorm.DB) error {
@@ -336,6 +363,33 @@ func (r *PostRepository) IsFavorited(postID, userID string) bool {
 	return count > 0
 }
 
+// IsFavoritedBatch 批量检查是否收藏（解决 N+1 问题）
+// 返回 map[postID]bool
+func (r *PostRepository) IsFavoritedBatch(postIDs []string, userID string) map[string]bool {
+	result := make(map[string]bool)
+	if len(postIDs) == 0 || userID == "" {
+		return result
+	}
+
+	// 初始化所有 postID 为 false
+	for _, postID := range postIDs {
+		result[postID] = false
+	}
+
+	// 一次性查询所有收藏记录
+	var favoritedPostIDs []string
+	r.db.Model(&model.Favorite{}).
+		Where("post_id IN ? AND user_id = ?", postIDs, userID).
+		Pluck("post_id", &favoritedPostIDs)
+
+	// 更新已收藏的帖子
+	for _, postID := range favoritedPostIDs {
+		result[postID] = true
+	}
+
+	return result
+}
+
 // IncrementViews 增加帖子观看量
 func (r *PostRepository) IncrementViews(postID string) error {
 	return r.db.Model(&model.Post{}).Where("id = ?", postID).