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/Utilities/MonthlyContributionStore.swift

@@ -1,33 +1,59 @@
 import Foundation
+import CoreData
 
+/// Per-source recurring monthly contribution amount.
+///
+/// Backed by the `InvestmentSource.monthlyContribution` Core Data attribute so the value
+/// syncs across devices via iCloud/CloudKit. Previously stored in `UserDefaults`, which is
+/// device-local and did NOT sync — `migrateIfNeeded(context:)` moves any legacy value over.
 enum MonthlyContributionStore {
-    private static let key = "monthlyContributions"
+    /// Legacy UserDefaults key (pre-iCloud). Only read once during migration.
+    private static let legacyKey = "monthlyContributions"
+
+    private static var viewContext: NSManagedObjectContext { CoreDataStack.shared.viewContext }
 
     static func contribution(for sourceId: UUID) -> Decimal? {
-        let dict = load()
-        guard let raw = dict[sourceId.uuidString] else { return nil }
-        return Decimal(raw)
+        guard let source = fetchSource(sourceId),
+              let amount = source.monthlyContribution?.decimalValue,
+              amount > 0 else { return nil }
+        return amount
     }
 
     static func setContribution(_ amount: Decimal?, for sourceId: UUID) {
-        var dict = load()
+        guard let source = fetchSource(sourceId) else { return }
         if let amount, amount > 0 {
-            dict[sourceId.uuidString] = NSDecimalNumber(decimal: amount).doubleValue
+            source.monthlyContribution = NSDecimalNumber(decimal: amount)
         } else {
-            dict.removeValue(forKey: sourceId.uuidString)
+            source.monthlyContribution = nil
         }
-        save(dict)
+        try? viewContext.save()
     }
 
-    private static func load() -> [String: Double] {
-        guard let data = UserDefaults.standard.data(forKey: key),
-              let decoded = try? JSONDecoder().decode([String: Double].self, from: data) else { return [:] }
-        return decoded
+    private static func fetchSource(_ id: UUID) -> InvestmentSource? {
+        let request = InvestmentSource.fetchRequest()
+        request.predicate = NSPredicate(format: "id == %@", id as CVarArg)
+        request.fetchLimit = 1
+        return try? viewContext.fetch(request).first
     }
 
-    private static func save(_ dict: [String: Double]) {
-        if let data = try? JSONEncoder().encode(dict) {
-            UserDefaults.standard.set(data, forKey: key)
+    // MARK: - Migration
+
+    /// One-time migration of legacy UserDefaults contributions into Core Data so they sync
+    /// via iCloud. Runs on every launch but is a no-op once the legacy key is cleared.
+    static func migrateIfNeeded(context: NSManagedObjectContext) {
+        guard let data = UserDefaults.standard.data(forKey: legacyKey),
+              let dict = try? JSONDecoder().decode([String: Double].self, from: data),
+              !dict.isEmpty else { return }
+
+        let sources = (try? context.fetch(InvestmentSource.fetchRequest())) ?? []
+        var changed = false
+        for source in sources where source.monthlyContribution == nil {
+            if let raw = dict[source.id.uuidString], raw > 0 {
+                source.monthlyContribution = NSDecimalNumber(value: raw)
+                changed = true
+            }
         }
+        if changed { try? context.save() }
+        UserDefaults.standard.removeObject(forKey: legacyKey)
     }
 }