🔥 Finish Cart implementation

- Use Select component in CartItem to change quantity
- Visual update when removing or changing an item quantity
- API: Remove Cart item action
- API: Handle Cart item adding and updating (quantity)

src/style/pages/_shop.scss

@@ -3,10 +3,8 @@
 
     // Cart
     .cart {
-        // display: flex;
-        // display: none;
         position: fixed;
-        z-index: 100;
+        z-index: 101;
         top: 72px;
         right: 0;
         width: 100%;
@@ -25,7 +23,7 @@
     .shop-location {
         display: flex;
         position: fixed;
-        z-index: 20;
+        z-index: 100;
         top: 18px;
         left: 20px;
         right: 20px;