platos: segundo plato por comida (ensalada + salmon)

- MealSlot.secondaryDishId (opcional, aditivo CloudKit); se limpia al
  sustituir/quitar/vaciar/marcar comer fuera y viaja en swaps, copia de
  semana anterior, undo y snapshot KV de iCloud (retrocompatible)
- Picker de hueco lleno: toggle "anadir como segundo plato" + boton para
  quitarlo; HomeViewModel.assignSecondaryDish/removeSecondaryDish
- Se muestra "Plato + Segundo" en calendario, widget y export; la lista
  de la compra incluye los ingredientes del segundo; stats lo cuentan
- Evento analytics secondary_dish_added; strings en 6 idiomas

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013H6bXqGX1ygwib1Dm3n3UG

MealMood/Views/Shopping/ShoppingListView.swift

@@ -34,10 +34,12 @@ struct ShoppingListView: View {
             ($0.dayOfWeek, $0.mealType) < ($1.dayOfWeek, $1.mealType)
         }
         for slot in sortedSlots {
-            guard let dishId = slot.dishId, !seen.contains(dishId),
-                  let dish = allDishes.first(where: { $0.id == dishId }) else { continue }
-            seen.insert(dishId)
-            result.append(dish)
+            for dishId in [slot.dishId, slot.secondaryDishId].compactMap({ $0 }) {
+                guard !seen.contains(dishId),
+                      let dish = allDishes.first(where: { $0.id == dishId }) else { continue }
+                seen.insert(dishId)
+                result.append(dish)
+            }
         }
         return result
     }