feat: aggrega duplicati nella lista della spesa con quantità

Quando si genera la lista dal piano pasti, gli alimenti ripetuti in
più giorni o slot vengono aggregati in un unico elemento con contatore.
Es. zucchine lunedì + mercoledì → "zucchine (x2)".

- ShoppingItem: aggiunto campo quantity (default 1, persistito in JSON)
- ShoppingListProvider.addAll: conta le occorrenze per nome
  (case-insensitive) e crea un ShoppingItem con quantity = conteggio
- ShoppingItemTile: mostra "(xN)" colorato in primary quando quantity > 1,
  diventa muted insieme al nome quando l'elemento è completato

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/features/shopping_list/models/shopping_item.dart

@@ -2,29 +2,34 @@ class ShoppingItem {
   final String id;
   final String name;
   final bool checked;
+  final int quantity;
 
   const ShoppingItem({
     required this.id,
     required this.name,
     this.checked = false,
+    this.quantity = 1,
   });
 
-  ShoppingItem copyWith({String? id, String? name, bool? checked}) =>
+  ShoppingItem copyWith({String? id, String? name, bool? checked, int? quantity}) =>
       ShoppingItem(
         id: id ?? this.id,
         name: name ?? this.name,
         checked: checked ?? this.checked,
+        quantity: quantity ?? this.quantity,
       );
 
   Map<String, dynamic> toJson() => {
         'id': id,
         'name': name,
         'checked': checked,
+        'quantity': quantity,
       };
 
   factory ShoppingItem.fromJson(Map<String, dynamic> json) => ShoppingItem(
         id: json['id'] as String,
         name: json['name'] as String,
         checked: json['checked'] as bool? ?? false,
+        quantity: json['quantity'] as int? ?? 1,
       );
 }

lib/features/shopping_list/presentation/widgets/shopping_item_tile.dart

@@ -32,14 +32,33 @@ class ShoppingItemTile extends StatelessWidget {
               ),
             ),
             Expanded(
-              child: Text(
-                item.name,
-                style: item.checked
-                    ? theme.textTheme.bodyMedium?.copyWith(
-                        decoration: TextDecoration.lineThrough,
-                        color: muted,
-                      )
-                    : theme.textTheme.bodyMedium,
+              child: Row(
+                children: [
+                  Expanded(
+                    child: Text(
+                      item.name,
+                      style: item.checked
+                          ? theme.textTheme.bodyMedium?.copyWith(
+                              decoration: TextDecoration.lineThrough,
+                              color: muted,
+                            )
+                          : theme.textTheme.bodyMedium,
+                    ),
+                  ),
+                  if (item.quantity > 1)
+                    Padding(
+                      padding: const EdgeInsets.only(left: 6),
+                      child: Text(
+                        '(x${item.quantity})',
+                        style: theme.textTheme.bodySmall?.copyWith(
+                          color: item.checked
+                              ? muted
+                              : theme.colorScheme.primary,
+                          fontWeight: FontWeight.w600,
+                        ),
+                      ),
+                    ),
+                ],
               ),
             ),
             IconButton(

lib/features/shopping_list/providers/shopping_list_provider.dart

@@ -49,16 +49,26 @@ class ShoppingListProvider extends ChangeNotifier {
 
   void addAll(List<String> names) {
     final existing = _items.map((i) => i.name.toLowerCase()).toSet();
-    final seen = <String>{};
-    final toAdd = <ShoppingItem>[];
+
+    // Conta le occorrenze mantenendo il nome nella sua forma originale (prima occorrenza)
+    final counts = <String, int>{};
+    final canonical = <String, String>{};
     for (final name in names) {
       final key = name.toLowerCase().trim();
-      if (key.isNotEmpty && !existing.contains(key) && seen.add(key)) {
-        toAdd.add(ShoppingItem(
-          id: '${DateTime.now().millisecondsSinceEpoch}_${seen.length}',
-          name: name.trim(),
-        ));
-      }
+      if (key.isEmpty) continue;
+      counts[key] = (counts[key] ?? 0) + 1;
+      canonical.putIfAbsent(key, () => name.trim());
+    }
+
+    final toAdd = <ShoppingItem>[];
+    var i = 0;
+    for (final entry in counts.entries) {
+      if (existing.contains(entry.key)) continue;
+      toAdd.add(ShoppingItem(
+        id: '${DateTime.now().millisecondsSinceEpoch}_${i++}',
+        name: canonical[entry.key]!,
+        quantity: entry.value,
+      ));
     }
     if (toAdd.isEmpty) return;
     _items = [..._items, ...toAdd];