Use the tzgyn relay as the default backend

The CLI and iOS app now point at share.tzgyn.dev:9009 instead of the upstream croc relay. Both were verified against the deployed relay; local relays remain available through --relay and the app's Relay setting.

apps/ios/Share/RoomView.swift

@@ -164,7 +164,7 @@ struct RoomView: View {
       HStack(spacing: 6) {
         Image(systemName: "network")
           .font(.system(size: 10, weight: .semibold))
-        Text(status.relay.isEmpty ? "public relay" : status.relay)
+        Text(status.relay.isEmpty ? "tzgyn relay" : status.relay)
           .lineLimit(1)
           .truncationMode(.middle)
       }

apps/ios/Share/SelfTest.swift

@@ -1,4 +1,5 @@
 import Foundation
+import Share
 import SwiftUI
 
 /// A headless-ish smoke test driven by launch arguments:
@@ -18,7 +19,7 @@ enum SelfTest {
   static func runIfRequested(model: AppModel) {
     let args = ProcessInfo.processInfo.arguments
     guard !started else { return }
-    let relay = value(after: "-shareSelfTestRelay", in: args) ?? "127.0.0.1:9009"
+    let relay = value(after: "-shareSelfTestRelay", in: args) ?? ShareRelayDefault()
     let code = value(after: "-shareSelfTestCode", in: args)
       ?? (args.contains("-shareSelfTestSend")
           ? "1234-selftest-send-apple"

apps/ios/Share/SetupView.swift

@@ -286,14 +286,14 @@ struct SetupView: View {
             Image(systemName: "info.circle")
               .font(.system(size: 11, weight: .semibold))
               .padding(.top, 1)
-            Text("Use your Mac's LAN address, like 192.168.1.20:9009, when you run `share relay` there. Leave it empty for the public relay.")
+            Text("Use your Mac's LAN address, like 192.168.1.20:9009, when you run `share relay` there. Leave it empty for the tzgyn relay.")
               .font(.caption)
               .fixedSize(horizontal: false, vertical: true)
           }
           .foregroundStyle(Theme.tertiaryText)
 
           if !model.relay.isEmpty {
-            Button("Use public relay") {
+            Button("Use tzgyn relay") {
               model.relay = ShareRelayDefault()
             }
             .buttonStyle(QuietButtonStyle(tint: Theme.mint))