Fix the iPhone review's findings

- Cancelling (Change headset, Forget) invalidates the attempt in flight; a
  connection only becomes the app's once every step finished for it.
- A server that stops while the tunnel opens is noticed (exit callbacks are
  synchronised and replayed), and the app isn't left showing a dead page.
- The port is read only once the digits are complete, and range-checked.
- Other versions in ~/.cache/frame-control stay unless untouched for 14 days,
  so a second phone or iPad isn't cut off.
- The key is appended on its own line even if authorized_keys lacks a final
  newline.
- The app checks every 20 s, and on returning to the foreground, that the SSH
  session still answers, and reconnects if not.
- The ssh stand-in runs the command as its own process group and passes a
  TERM on to all of it, so a live-video ffmpeg stops with its stream.
- Touch screens show the library's Play buttons (the rule now follows the
  base one); the failure screen only says it's retrying when it is; the page
  says the app reconnects rather than naming a desktop menu.

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

ui/local-bin/ssh

@@ -13,4 +13,17 @@ done
 [ $# -gt 0 ] && shift  # the host alias
 cd "$HOME" || exit 255
 [ $# -eq 0 ] && exit 0  # -N: nothing to run
-exec "${SHELL:-/bin/sh}" -c "$*"
+# Stopping ssh ends everything the command started (sshd hangs up the session).
+# To do the same, run COMMAND as its own process group and pass on a TERM, HUP
+# or INT to all of it, so e.g. a live-video ffmpeg can't outlive its stream.
+set -m  # job control: the background job gets its own process group, and keeps stdin
+"${SHELL:-/bin/sh}" -c "$*" &
+child=$!
+trap 'kill -TERM -- "-$child" 2>/dev/null' TERM HUP INT
+wait "$child"
+status=$?
+while kill -0 "$child" 2>/dev/null; do  # a trapped signal ends `wait` early
+  wait "$child"
+  status=$?
+done
+exit "$status"