iPhone and iPad app: the same features, served from the Frame

An iPhone can't run Python or ssh, but the Frame can. The app (ios/, SwiftUI)
connects with its own SSH key (Citadel), copies the server and helpers to
~/.cache/frame-control/<version> on the Frame once per version, starts
ui/server.py there with FRAME_LOCAL=1 on the Frame's 127.0.0.1, and shows the
page through an SSH tunnel. The server exits when the phone disconnects.

Server: FRAME_LOCAL=1 puts ui/local-bin on PATH, whose ssh stand-in runs each
`ssh frame COMMAND` locally (and serves as rsync's transport), so desktop and
phone share one code path. Android display goes through podman exec there, as
the Frame has no adb. FRAME_UI_KEY replaces the fixed X-Frame-UI value with a
per-session key. Power actions take the Developer Mode password via sudo -S.
--port 0 now prints the port it took.

Page: a bottom tab bar and safe areas on phones, Play buttons visible on touch
screens, saving through the share sheet, SSH/SFTP/Steam Link/remote desktop
opening in their iOS apps, and a password dialog for power.

App: pairing with the Developer Mode password once (never stored) or with a
key the user adds; host key pinned on first use; plain-language connection
errors with quiet retries; frame-control://install links; alerts and confirms.

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

README.md

@@ -98,6 +98,9 @@ already ships (sideloading a game copies Valve's own devkit scripts to
 | **Linux** (x64) | [AppImage](https://github.com/saphid/steam-frame/releases/latest/download/Frame-Control-linux-x86_64.AppImage) · [.deb](https://github.com/saphid/steam-frame/releases/latest/download/Frame-Control-linux-amd64.deb) | `ssh` (most desktops have it) |
 | **Linux** (arm64) | [AppImage](https://github.com/saphid/steam-frame/releases/latest/download/Frame-Control-linux-arm64.AppImage) · [.deb](https://github.com/saphid/steam-frame/releases/latest/download/Frame-Control-linux-arm64.deb) | `ssh`, and `adb` for Android apps (`sudo apt install adb`) |
 
+**iPhone and iPad:** the same features from your phone, with nothing to install on
+a computer. Build it from [`ios/`](ios) in Xcode; see [docs/iphone.md](docs/iphone.md).
+
 The app brings its own Python and `adb`; SSH is built into macOS and Windows.
 Google doesn't publish `adb` for arm64 Linux, so that build uses your
 distribution's. If you already have `adb`, the app uses yours.