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>

Services/SFTPService.swift

@@ -0,0 +1,100 @@
+import Foundation
+import NIO
+import Citadel
+
+final class SFTPService: NASTransferProtocol {
+    private var client: SSHClient?
+    private var sftp: SFTPClient?
+    private(set) var isConnected: Bool = false
+
+    func connect(to host: String, port: Int, username: String, password: String) async throws {
+        do {
+            let c = try await SSHClient.connect(
+                host: host,
+                port: port,
+                authenticationMethod: .passwordBased(username: username, password: password),
+                hostKeyValidator: .acceptAnything(),
+                reconnect: .never
+            )
+            let sftpClient = try await c.openSFTP()
+            self.client = c
+            self.sftp = sftpClient
+            self.isConnected = true
+        } catch {
+            throw BackupError.connectionFailed(host)
+        }
+    }
+
+    func disconnect() {
+        Task {
+            try? await sftp?.close()
+            client = nil
+        }
+        sftp = nil
+        isConnected = false
+    }
+
+    func listDirectory(at path: String) async throws -> [NASItem] {
+        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
+        do {
+            let batches = try await sftp.listDirectory(atPath: path)
+            // listDirectory returns [SFTPMessage.Name]; each Name contains multiple SFTPPathComponent
+            let components = batches.flatMap { $0.components }
+            return components.compactMap { component -> NASItem? in
+                guard component.filename != "." && component.filename != ".." else { return nil }
+                let fullPath = path.hasSuffix("/")
+                    ? "\(path)\(component.filename)"
+                    : "\(path)/\(component.filename)"
+                let isDir = component.attributes.permissions.map { ($0 & 0o170000) == 0o040000 } ?? false
+                return NASItem(
+                    name: component.filename,
+                    path: fullPath,
+                    isDirectory: isDir,
+                    size: Int64(component.attributes.size ?? 0),
+                    modifiedDate: nil
+                )
+            }
+        } catch {
+            throw BackupError.directoryListFailed(path)
+        }
+    }
+
+    func createDirectory(at path: String) async throws {
+        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
+        do {
+            try await sftp.createDirectory(atPath: path)
+        } catch {
+            throw BackupError.directoryCreateFailed(path)
+        }
+    }
+
+    func fileExists(at remotePath: String) async throws -> Bool {
+        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
+        do {
+            _ = try await sftp.getAttributes(at: remotePath)
+            return true
+        } catch {
+            return false
+        }
+    }
+
+    func upload(localURL: URL, remotePath: String, progress: @escaping (Int64, Int64) -> Void) async throws {
+        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
+        let filename = localURL.lastPathComponent
+        do {
+            let data = try Data(contentsOf: localURL)
+            let total = Int64(data.count)
+            progress(0, total)
+            try await sftp.withFile(
+                filePath: remotePath,
+                flags: [.write, .create, .truncate]
+            ) { file in
+                var buffer = ByteBuffer(data: data)
+                try await file.write(buffer, at: 0)
+            }
+            progress(total, total)
+        } catch {
+            throw BackupError.uploadFailed(filename, underlying: error)
+        }
+    }
+}