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/App/FrameControlApp.swift

@@ -14,6 +14,11 @@ struct FrameControlApp: App {
                     // and connect to FRAME_TEST_HOST with it (`simctl launch` passes
                     // SIMCTL_CHILD_FRAME_TEST_HOST through as FRAME_TEST_HOST).
                     print("FRAME_CONTROL_KEY: \(model.authorizedKeysLine)")
+                    // FRAME_TEST_PAIR="host|user|password" runs the real password pairing.
+                    if model.settings == nil, let pair = ProcessInfo.processInfo.environment["FRAME_TEST_PAIR"] {
+                        let f = pair.components(separatedBy: "|")
+                        if f.count == 3 { await model.pair(host: f[0], user: f[1], password: f[2]); return }
+                    }
                     if model.settings == nil, let host = ProcessInfo.processInfo.environment["FRAME_TEST_HOST"] {
                         await model.useKey(host: host, user: "steamos")
                         return