added backend and 2 endpoints fetch

backend/model/category.go

@@ -0,0 +1,8 @@
+package model
+
+type Category struct {
+	ID            string        `json:"id"`
+	Icon          string        `json:"icon"`
+	Title         string        `json:"title"`
+	Subcategories []Subcategory `json:"subcategories"`
+}