category tree api

.../java/com/example/freshonline/FreshOnlineApplication.java

...ain/java/com/example/freshonline/constants/Constants.java

...om/example/freshonline/controller/CategoryController.java

src/main/java/com/example/freshonline/dao/CartMapper.java

...main/java/com/example/freshonline/dao/CategoryMapper.java

...main/java/com/example/freshonline/dao/FavoriteMapper.java

src/main/java/com/example/freshonline/dao/OrderMapper.java

...java/com/example/freshonline/dao/PaymentMethodMapper.java

...in/java/com/example/freshonline/dao/SaledGoodsMapper.java

.../java/com/example/freshonline/dao/StockedGoodsMapper.java

src/main/java/com/example/freshonline/dao/UserMapper.java

...in/java/com/example/freshonline/dto/CategoryTreeNode.java

src/main/java/com/example/freshonline/model/Cart.java

src/main/java/com/example/freshonline/model/CartExample.java

src/main/java/com/example/freshonline/model/Category.java

...n/java/com/example/freshonline/model/CategoryExample.java

src/main/java/com/example/freshonline/model/Favorite.java

...n/java/com/example/freshonline/model/FavoriteExample.java

src/main/java/com/example/freshonline/model/Order.java

...main/java/com/example/freshonline/model/OrderExample.java