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/Stats/StatsView.swift

@@ -172,6 +172,7 @@ struct StatsView: View {
         for plan in weekPlans {
             for slot in plan.slotList {
                 if let id = slot.dishId { counts[id, default: 0] += 1 }
+                if let id = slot.secondaryDishId { counts[id, default: 0] += 1 }
             }
         }
         return counts
@@ -197,8 +198,10 @@ struct StatsView: View {
         var counts: [UUID: Int] = [:]
         for plan in weekPlans {
             for slot in plan.slotList {
-                guard let dishId = slot.dishId, let dish = dishMap[dishId] else { continue }
-                for tagId in dish.tagIds { counts[tagId, default: 0] += 1 }
+                for dishId in [slot.dishId, slot.secondaryDishId].compactMap({ $0 }) {
+                    guard let dish = dishMap[dishId] else { continue }
+                    for tagId in dish.tagIds { counts[tagId, default: 0] += 1 }
+                }
             }
         }
         return counts