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/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"