SimpleX names v2: Android, desktop and iOS UIs

The names hub and the buy / gift / receive / renew / recovery-key flows
across the Kotlin multiplatform app and the iOS Swift app. Stacked on the
core PR. iOS is written but unbuilt: it needs a Mac build (no iOS job in
CI) and a core lib rebuilt from the new simplexmq pin; expect
MsgContent.assetTransfer exhaustiveness one-liners and a few accessor
fixes on first xcodebuild.

apps/ios/Shared/Views/UserSettings/SimplexNames/NameRecoveryKeyView.swift

@@ -0,0 +1,49 @@
+import SwiftUI
+import SimpleXChat
+
+// The recovery key for the user's names. For most users this is the only backup
+// they have of anything. The stakes are impersonation, not loss: whoever holds
+// it can point a name at their own address.
+struct NameRecoveryKeyView: View {
+    @State private var phrase: String? = nil
+    @State private var loadFailed = false
+    @State private var saved = false
+    @State private var revealed = false
+
+    var body: some View {
+        List {
+            Section { Text("These words control your names. Anyone who has them controls your names too.").foregroundColor(.secondary) }
+
+            if loadFailed {
+                Section { Text("Could not load your names. Check your connection and reopen this screen.").foregroundColor(.orange) }
+            } else if phrase == nil {
+                Section { Text("You will get a recovery key when you get your first name.").foregroundColor(.secondary) }
+            } else if !revealed {
+                Section {
+                    Button { revealed = true } label: { Label("Show recovery key", systemImage: "eye").foregroundColor(.accentColor) }
+                } footer: { Text("Make sure no one can see your screen.") }
+            } else {
+                Section("Your recovery key") {
+                    Text(phrase!).font(.body.monospaced()).fontWeight(.medium)
+                    Button("Copy") { UIPasteboard.general.string = phrase }.foregroundColor(.accentColor)
+                } footer: {
+                    Text("Write these words down and keep them somewhere safe and offline. Anyone who takes a photo of this screen can take your names.")
+                }
+                Section {
+                    if saved { Text("You marked this as saved.").foregroundColor(.secondary) }
+                    else { Button { markSaved() } label: { Label("I have saved it", systemImage: "checkmark").foregroundColor(.accentColor) } }
+                }
+            }
+
+            Section("If someone else gets this key") {
+                Text("They can point your name at their own profile, so people looking for you would find them instead.").foregroundColor(.red)
+            }
+        }
+        .navigationTitle("Recovery key")
+        .task {
+            if let r = await apiNameRecoveryKey() { phrase = r.phrase; saved = r.saved } else { loadFailed = true }
+        }
+    }
+
+    private func markSaved() { Task { if await apiNameRecoveryKeySaved() { saved = true } } }
+}