Sync monthly contributions y allocation targets vía iCloud (CoreData)

Ambos vivían en UserDefaults (device-local, no sincroniza). Migrados a atributos
CoreData en entidades ya syncable=YES, así que ahora sincronizan por CloudKit:

- InvestmentSource.monthlyContribution (Decimal, opcional)
- Category.allocationTarget (Double, opcional)

Los stores mantienen su API por UUID (0 cambios en call sites) pero ahora leen/escriben
del atributo CoreData vía fetch por id. migrateIfNeeded(context:) mueve una sola vez los
valores del diccionario UserDefaults legacy al modelo y borra la clave; enganchado en
CoreDataStack.loadPersistentStores junto a MonthlyCheckInStore.

DashboardLayoutStore se mantiene en UserDefaults a propósito (preferencia de UI por
dispositivo: el columnSpan solo aplica en iPad).

NOTA: requiere desplegar el schema CloudKit a producción (CD_monthlyContribution,
CD_allocationTarget) antes de que sincronice en TestFlight/App Store.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015qUZrBusG82T37R7PeokqJ

PortfolioJournal/Models/CoreData/Category+CoreDataClass.swift

@@ -14,6 +14,7 @@ public class Category: NSManagedObject, Identifiable {
     @NSManaged public var icon: String
     @NSManaged public var sortOrder: Int16
     @NSManaged public var createdAt: Date
+    @NSManaged public var allocationTarget: NSNumber?
     @NSManaged public var sources: NSSet?
 
     public override func awakeFromInsert() {

PortfolioJournal/Models/CoreData/InvestmentSource+CoreDataClass.swift

@@ -12,6 +12,7 @@ public class InvestmentSource: NSManagedObject, Identifiable {
     @NSManaged public var notificationFrequency: String
     @NSManaged public var customFrequencyMonths: Int16
     @NSManaged public var isActive: Bool
+    @NSManaged public var monthlyContribution: NSDecimalNumber?
     @NSManaged public var createdAt: Date
     @NSManaged public var category: Category?
     @NSManaged public var account: Account?

PortfolioJournal/Models/CoreData/PortfolioJournal.xcdatamodeld/PortfolioJournal.xcdatamodel/contents

@@ -25,6 +25,7 @@
         <relationship name="sources" optional="YES" toMany="YES" deletionRule="Cascade" destinationEntity="InvestmentSource" inverseName="account" inverseEntity="InvestmentSource"/>
     </entity>
     <entity name="Category" representedClassName="Category" syncable="YES">
+        <attribute name="allocationTarget" optional="YES" attributeType="Double" usesScalarValueType="NO"/>
         <attribute name="colorHex" attributeType="String" defaultValueString="#3B82F6"/>
         <attribute name="createdAt" optional="YES" attributeType="Date" usesScalarValueType="NO"/>
         <attribute name="icon" attributeType="String" defaultValueString="chart.pie.fill"/>
@@ -38,6 +39,7 @@
         <attribute name="customFrequencyMonths" attributeType="Integer 16" defaultValueString="1" usesScalarValueType="YES"/>
         <attribute name="id" optional="YES" attributeType="UUID" usesScalarValueType="NO"/>
         <attribute name="isActive" attributeType="Boolean" defaultValueString="YES" usesScalarValueType="YES"/>
+        <attribute name="monthlyContribution" optional="YES" attributeType="Decimal"/>
         <attribute name="name" attributeType="String" defaultValueString=""/>
         <attribute name="notificationFrequency" attributeType="String" defaultValueString="monthly"/>
         <relationship name="account" optional="YES" maxCount="1" deletionRule="Nullify" destinationEntity="Account" inverseName="sources" inverseEntity="Account"/>