1.6.0 #9: auto-backup programado a iCloud Drive/Archivos

El BackupService (export JSON v3 lossless a local + iCloud ubiquity, retención,
restore, premium-gated) ya existía de 1.1.0 pero solo era manual. Añadido lo automático:
- BackupService.runScheduledBackupIfNeeded() (config vía UserDefaults, gate por
  backupsEnabled+premium, respeta frecuencia).
- Disparo en foreground (scenePhase .active) en background queue.
- Frecuencia Off/Diario/Semanal/Mensual + fecha del último backup en Settings
  (SettingsViewModel.autoBackupFrequencyDays + updateAutoBackupFrequency).
- Strings en 7 idiomas.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L2p3gUZRNWW388rWFRjiU7

PortfolioJournal/ViewModels/SettingsViewModel.swift

@@ -36,6 +36,8 @@ class SettingsViewModel: ObservableObject {
     @Published var backupRetentionCount = 10
     @Published var backups: [BackupRecord] = []
     @Published var backupsEnabled = false
+    /// Auto-backup cadence in days: 0 = off, 1 = daily, 7 = weekly, 30 = monthly.
+    @Published var autoBackupFrequencyDays = 0
 
     // MARK: - Dependencies
 
@@ -96,6 +98,7 @@ class SettingsViewModel: ObservableObject {
         inputMode = InputMode(rawValue: settings.inputMode) ?? .simple
         backupRetentionCount = loadBackupRetention()
         backupsEnabled = loadBackupsEnabled()
+        autoBackupFrequencyDays = UserDefaults.standard.integer(forKey: "autoBackupFrequencyDays")
         if backupsEnabled {
             refreshBackups()
         } else {
@@ -395,6 +398,19 @@ class SettingsViewModel: ObservableObject {
         backups = BackupService.shared.listAllBackups(includeICloud: includeICloud)
     }
 
+    /// Auto-backup cadence (0 = off). Running one immediately when enabled gives
+    /// instant feedback that it works.
+    func updateAutoBackupFrequency(_ days: Int) {
+        guard backupsEnabled, isPremium else { return }
+        autoBackupFrequencyDays = days
+        UserDefaults.standard.set(days, forKey: "autoBackupFrequencyDays")
+        if days > 0 { createBackupNow() }
+    }
+
+    var lastAutoBackupDate: Date? {
+        UserDefaults.standard.object(forKey: "lastAutoBackupDate") as? Date
+    }
+
     func createBackupNow() {
         guard backupsEnabled, isPremium else { return }
         guard !isBackupInProgress else { return }