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/Views/Settings/SettingsView.swift

@@ -534,6 +534,27 @@ struct SettingsView: View {
                 }
             }
 
+            if viewModel.backupsEnabled {
+                Picker("Auto Backup", selection: Binding(
+                    get: { viewModel.autoBackupFrequencyDays },
+                    set: { viewModel.updateAutoBackupFrequency($0) }
+                )) {
+                    Text("Off").tag(0)
+                    Text("Daily").tag(1)
+                    Text("Weekly").tag(7)
+                    Text("Monthly").tag(30)
+                }
+                if let last = viewModel.lastAutoBackupDate {
+                    HStack {
+                        Text("Last auto backup")
+                        Spacer()
+                        Text(last, style: .date)
+                            .foregroundColor(.secondary)
+                    }
+                    .font(.caption)
+                }
+            }
+
             NavigationLink {
                 CategoriesView()
             } label: {