Refactor profile screen layout and user preference handling

App.js

@@ -138,6 +138,7 @@ export default function App() {
           onStartScan={() => setActiveTab('scan')}
           onOpenProfile={() => setActiveTab('profile')}
           onToggleItem={toggleListItem}
+          onChangeItemQuantity={changeListItemQuantity}
           onUpdateItemPrice={updateListItemPrice}
           preferences={preferences}
           lastDeletedItem={lastDeletedListItem}
@@ -269,6 +270,7 @@ export default function App() {
               ? {
                   ...item,
                   quantity: item.quantity + 1,
+                  checked: false,
                   packageQuantityGrams: item.packageQuantityGrams ?? product.packageQuantityGrams,
                   packageQuantityLabel: item.packageQuantityLabel ?? product.packageQuantityLabel,
                   servingQuantityGrams: item.servingQuantityGrams ?? product.servingQuantityGrams,
@@ -337,6 +339,17 @@ export default function App() {
     }));
   }
 
+  function changeListItemQuantity(itemId, change) {
+    setShoppingList((current) => {
+      const items = current.items.map((item) =>
+        item.id === itemId
+          ? { ...item, quantity: Math.max(1, (item.quantity || 1) + change) }
+          : item
+      );
+      return { ...current, items, estimatedTotal: calculateEstimatedTotal(items) };
+    });
+  }
+
   function deleteListItem(itemId) {
     const index = shoppingList.items.findIndex((item) => item.id === itemId);
     if (index < 0) return;