feat: Kisani rebrand, step-based onboarding flow, dark mode fixes

- Rename app to Kisani in all UI text and Face ID prompt
- Replace flat 2-state RootView with 5-step flow: ConnectView →
  LoginView → FolderSetupView → PhotoPermissionView → MainTabView
- Remove NavigationStack from LoginView (was causing nested-stack crash);
  drive navigation via ConnectionStore.isSessionActive
- Add FolderSetupView and PhotoPermissionView onboarding screens with
  step indicator (2/3, 3/3), spring entrance animations, and UGreen
  connection chip
- Fix dark mode button invisibility: PrimaryButtonStyle and PillButtonStyle
  now use AppTheme.inkInverse; GhostButtonStyle border uses ink.opacity(0.25)
- Add AppTheme.inkInverse adaptive token (dark bg ink on dark, white on light)
- Add ConnectionStore.isSessionActive (non-persisted) and
  onboardingPhotoShown (UserDefaults-persisted)
- Add os_log logging in LoginViewModel at auth start/success/failure
- Remove dead Help button from ConnectView
- UGreenCompatibilityBadge, KeychainStore, SavedConnections, extensions,
  PrivacyInfo.xcprivacy, unit test target and test stubs
- AppTheme: full UIColor dynamic provider tokens for dark/light adaptive color
- AppearanceMode enum + segmented picker in SettingsView
- BackupView: enlarged ring, removed options card and linear progress bar
- HistoryView: duration and bytes formatting, improved typography hierarchy

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Services/BackupEngine.swift

@@ -1,5 +1,8 @@
 import Foundation
 import UserNotifications
+import os.log
+
+private let logger = Logger(subsystem: "com.albert.nasbackup", category: "BackupEngine")
 
 @MainActor
 final class BackupEngine: ObservableObject {
@@ -7,11 +10,30 @@ final class BackupEngine: ObservableObject {
 
     @Published private(set) var job: BackupJob = BackupJob()
 
-    private let photoService: PhotoLibraryProtocol = PhotoLibraryService()
+    private let photoService: PhotoLibraryProtocol
+    private let transferFactory: (NASProtocol) -> any NASTransferProtocol
     private var activeTransfer: (any NASTransferProtocol)?
     private var isCancelled = false
 
-    private init() {}
+    private init(
+        photos: PhotoLibraryProtocol = PhotoLibraryService(),
+        transferFactory: @escaping (NASProtocol) -> any NASTransferProtocol = { proto in
+            switch proto {
+            case .smb:  return SMBService()
+            case .sftp: return SFTPService()
+            }
+        }
+    ) {
+        self.photoService = photos
+        self.transferFactory = transferFactory
+    }
+
+    static func testInstance(
+        transfer: any NASTransferProtocol,
+        photos: PhotoLibraryProtocol
+    ) -> BackupEngine {
+        BackupEngine(photos: photos, transferFactory: { _ in transfer })
+    }
 
     func run(
         connection: NASConnection,
@@ -36,11 +58,7 @@ final class BackupEngine: ObservableObject {
         let assets = photoService.fetchAssets(filter: filter)
 
         // 2. Connect to NAS
-        let transfer: any NASTransferProtocol
-        switch connection.nasProtocol {
-        case .smb:  transfer = SMBService()
-        case .sftp: transfer = SFTPService()
-        }
+        let transfer = transferFactory(connection.nasProtocol)
 
         try await transfer.connect(
             to: host,
@@ -102,6 +120,7 @@ final class BackupEngine: ObservableObject {
                 job.fileCompleted(skipped: false)
                 uploaded += 1
             } catch {
+                logger.error("Upload failed for \(asset.filename, privacy: .public): \(error.localizedDescription, privacy: .public)")
                 job.fileFailed()
                 failed += 1
             }