Store shots: pass the relay to the app when signing in to an account

Test launches default to http://127.0.0.1:9 so no suite reaches
production by accident. The shot test set -FNMSGServer only for a
throwaway sign-up, so signing in to a named account hit the dead
loopback and failed with "Could not connect to the server".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

UITests/AppStoreShotsUITests.swift

@@ -52,7 +52,9 @@ final class AppStoreShotsUITests: XCTestCase {
 
         let app = XCUIApplication.underTest()
         app.launchArguments = ["-FNMSGResetState"]
-        if !haveAccount {
+        // A test launch defaults to a dead loopback address so no suite
+        // reaches production by accident. The store set names its relay.
+        if !signUpRelay.isEmpty {
             app.launchArguments += ["-FNMSGServer", signUpRelay]
         }
         app.launch()