Initial scaffold — NASBackup iOS app

Full project scaffold: XcodeGen project.yml, Core models/protocols/errors,
SMBService (kishikawakatsumi/SMBClient), SFTPService (Citadel 0.9.2),
PhotoLibraryService, LANMonitor, BackupEngine, BackgroundTaskManager,
all feature UIs (Login, Connect, Browse, Backup, History, Settings),
Shared components and theme. Builds clean with zero errors.

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

Features/Login/LoginViewModel.swift

@@ -0,0 +1,36 @@
+import Foundation
+import LocalAuthentication
+
+@MainActor
+final class LoginViewModel: ObservableObject {
+    @Published var showMoreSheet = false
+    @Published var isAuthenticating = false
+    @Published var authError: String? = nil
+
+    var onAuthenticated: (() -> Void)?
+
+    func authenticateWithFaceID() {
+        isAuthenticating = true
+        authError = nil
+        let context = LAContext()
+        var error: NSError?
+        guard context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: &error) else {
+            authError = "Face ID not available"
+            isAuthenticating = false
+            return
+        }
+        context.evaluatePolicy(
+            .deviceOwnerAuthenticationWithBiometrics,
+            localizedReason: "Sign in to NASBackup"
+        ) { [weak self] success, evalError in
+            Task { @MainActor in
+                self?.isAuthenticating = false
+                if success {
+                    self?.onAuthenticated?()
+                } else {
+                    self?.authError = evalError?.localizedDescription ?? "Authentication failed"
+                }
+            }
+        }
+    }
+}