Add a native iOS client for relay-based file sharing

The SwiftUI app bundles the Go swarm engine through gomobile, so an iPhone is a real peer using the existing PAKE handshake, chunk verification, and relay fallback. XcodeGen builds the project and devicectl installs it on the paired phone.

apps/ios/Share/Models.swift

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+import Foundation
+
+/// Which side of the room the setup screen is preparing. Once a room is
+/// running the distinction only changes labels: every peer can send and
+/// receive, just like the CLI.
+enum RoomMode: String, CaseIterable, Identifiable {
+  case send
+  case receive
+
+  var id: String { rawValue }
+
+  var title: String {
+    switch self {
+    case .send: return "Send"
+    case .receive: return "Receive"
+    }
+  }
+
+  var icon: String {
+    switch self {
+    case .send: return "arrow.up.circle.fill"
+    case .receive: return "arrow.down.circle.fill"
+    }
+  }
+}
+
+/// One file's progress as reported by the Go engine. The JSON field names
+/// match `swarm.FileStatus`; no conversion layer is needed.
+struct FileProgress: Codable, Identifiable, Hashable {
+  let name: String
+  let size: Int64
+  let haveChunks: Int64
+  let totalChunks: Int64
+  let complete: Bool
+
+  var id: String { name }
+
+  var fraction: Double {
+    guard totalChunks > 0 else { return 0 }
+    return min(1, max(0, Double(haveChunks) / Double(totalChunks)))
+  }
+
+  var formattedSize: String {
+    ByteCountFormatter.string(fromByteCount: size, countStyle: .file)
+  }
+}
+
+/// The whole room snapshot decoded from `ShareSession.statusJSON()`. The
+/// Go bridge keeps the same shape across launches so the UI never has to
+/// know about gomobile objects beyond the session itself.
+struct RoomStatus: Codable {
+  var code: String
+  var relay: String
+  var outDir: String
+  var running: Bool
+  var peers: Int
+  var files: [FileProgress]
+  var error: String?
+
+  var allComplete: Bool {
+    !files.isEmpty && files.allSatisfy(\.complete)
+  }
+
+  var receivedFiles: [FileProgress] {
+    files.filter(\.complete)
+  }
+}
+
+/// A file that has already been copied into the app's seed directory.
+/// Holding the copied URL (rather than the security-scoped picker URL)
+/// means the Go engine can keep reading it after the picker goes away.
+struct PickedFile: Identifiable, Hashable {
+  let id = UUID()
+  let url: URL
+  let name: String
+  let size: Int64
+
+  var formattedSize: String {
+    ByteCountFormatter.string(fromByteCount: size, countStyle: .file)
+  }
+}