Added "create list" handler, service + repository

internal/domain/list.go

@@ -0,0 +1,37 @@
+package domain
+
+import (
+	"context"
+	"errors"
+	"time"
+)
+
+type List struct {
+	ID        string    `json:"id"`
+	Name      string    `json:"name"`
+	CreatedAt time.Time `json:"created_at"`
+}
+
+type ListRepository interface {
+	CreateList(ctx context.Context, name string, userIDs []string) (*List, error)
+}
+
+type ListService struct {
+	repo ListRepository
+}
+
+func NewListService(repo ListRepository) *ListService {
+	return &ListService{repo: repo}
+}
+
+func (s *ListService) Create(ctx context.Context, name string, userIDs []string) (*List, error) {
+	if len(userIDs) == 0 {
+		return nil, errors.New("users must have at least one associated user")
+	}
+
+	if name == "" {
+		return nil, errors.New("list name must not be empty")
+	}
+
+	return s.repo.CreateList(ctx, name, userIDs)
+}