Initial Marktplaats SDK scaffold

Clone the twdehands SDK into mrktplaats and retarget naming and defaults for app.marktplaats.nl while keeping the same request/response bodies and endpoint behavior.

categories.go

@@ -0,0 +1,64 @@
+package mrktplaats
+
+import (
+	"context"
+	"fmt"
+)
+
+// CategoryService handles category browsing.
+type CategoryService struct {
+	t *transport
+}
+
+// Category represents a node in the category tree (snake_case API3 format).
+type Category struct {
+	CategoryID          int               `json:"category_id"`
+	Name                string            `json:"name"`
+	Children            []Category        `json:"children"`
+	PlaceAdAllowed      bool              `json:"place_ad_allowed"`
+	NumberOfImages      int               `json:"number_of_images"`
+	RunningSubscriptions []any            `json:"running_subscriptions"`
+	FeaturesDuration    map[string]int    `json:"features_duration"`
+	SYIAttributes       []any             `json:"syi_attributes"`
+}
+
+// CategoriesResponse is the full category tree.
+type CategoriesResponse struct {
+	Categories []Category `json:"categories"`
+}
+
+// CategoryBucket groups related subcategories.
+type CategoryBucket struct {
+	ID         int              `json:"id"`
+	Name       string           `json:"name"`
+	Categories []BucketCategory `json:"categories"`
+}
+
+// BucketCategory is a leaf category within a bucket.
+type BucketCategory struct {
+	ID        int    `json:"id"`
+	Key       string `json:"key"`
+	ParentID  int    `json:"parentId"`
+	ParentKey string `json:"parentKey"`
+	Name      string `json:"name"`
+	ShortName string `json:"shortName"`
+}
+
+// All returns the full category tree.
+func (s *CategoryService) All(ctx context.Context) (*CategoriesResponse, error) {
+	var resp CategoriesResponse
+	if err := s.t.get(ctx, "/api3/categories.json", nil, &resp); err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+
+// Buckets returns the subcategory buckets for a parent category.
+func (s *CategoryService) Buckets(ctx context.Context, categoryID int) ([]CategoryBucket, error) {
+	path := fmt.Sprintf("/app/l1/v1/category-buckets/%d", categoryID)
+	var resp []CategoryBucket
+	if err := s.t.get(ctx, path, nil, &resp); err != nil {
+		return nil, err
+	}
+	return resp, nil
+}