iPhone app: test pairing and power against a Holo Core stand-in

Valve publishes no Steam Frame OS image, so tests/frame-container builds the
Frame's SSH surface on Valve and Collabora's Holo Core aarch64 base: a
steamos user with a password and sudo, OpenSSH with keys and passwords,
Python, and a systemctl that only records requests.

Against it from the Simulator: password pairing, the host-key pin, the power
password check. Found and fixed: a changed host key or a refused login said
"Can't reach the Frame" and retried forever; they now say "Pair with the
Frame again" and offer that. The server's key rejection now says the header
may be wrong, not only missing.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

ios/FrameControl/Views/RootView.swift

@@ -12,7 +12,7 @@ struct RootView: View {
             case .connecting(let step):
                 ConnectingView(step: step, host: model.settings?.host) { model.showSetup() }
             case .failed(let message):
-                FailedView(message: message, canRetry: model.settings != nil, retrying: model.retrying,
+                FailedView(message: message, canRetry: model.settings != nil, retrying: model.retrying, needsPairing: model.needsPairing,
                            retry: { Task { await model.connect() } }, change: { model.showSetup() })
             case .ready(let url):
                 WebShell(url: url, model: model).ignoresSafeArea()
@@ -51,19 +51,23 @@ struct FailedView: View {
     let message: String
     let canRetry: Bool
     let retrying: Bool
+    let needsPairing: Bool
     let retry: () -> Void
     let change: () -> Void
 
     var body: some View {
         VStack(spacing: 16) {
-            Image(systemName: "wifi.exclamationmark").font(.system(size: 44)).foregroundStyle(.orange)
-            Text("Can't reach the Frame").font(.title3.bold())
+            Image(systemName: needsPairing ? "lock.trianglebadge.exclamationmark" : "wifi.exclamationmark")
+                .font(.system(size: 44)).foregroundStyle(.orange)
+            Text(needsPairing ? "Pair with the Frame again" : "Can't reach the Frame").font(.title3.bold())
             Text(message).multilineTextAlignment(.center).foregroundStyle(Color.frameMuted)
             if retrying { Text("Trying again every few seconds.").font(.footnote).foregroundStyle(Color.frameMuted) }
-            if canRetry {
+            if needsPairing {
+                Button("Pair again", action: change).buttonStyle(.borderedProminent).controlSize(.large)
+            } else if canRetry {
                 Button("Try again", action: retry).buttonStyle(.borderedProminent).controlSize(.large)
             }
-            Button(canRetry ? "Change headset" : "Back", action: change)
+            if !needsPairing { Button(canRetry ? "Change headset" : "Back", action: change) }
         }
         .padding(32)
         .frame(maxWidth: 480)