PairSheet is a `Form` with two `TextField`s. On tvOS the focus engine drives
those natively, but on iOS/macOS a controller cannot reach a text field, type
into it, or press the button underneath — so for anyone in the console UI,
pairing (the ONE thing between a fresh install and a first stream) ended at
"now touch the screen".
GamepadPairView is the same ceremony in the gamepad UI's own vocabulary: the
vertical focus list the settings and add-host screens use, A on a field to
open GamepadKeyboard in a bottom tray, B to peel one layer. It mirrors
GamepadAddHostView field for field, because it is the same interaction and
someone who has added a host should recognise it immediately.
The ceremony itself moved to a shared `PairCeremony` used by both
presentations, so they can never disagree about what a wrong PIN means, what
a host rejection says, or when a late result must be discarded.
On iOS it is a shell layer like settings and add-host, and it LEADS the
shell's screen order: it blocks a connect the user already asked for and can
be raised from on top of the library (launching a title on an unpaired host),
so it has to win; backing out reveals whatever it interrupted. macOS has no
shell, so its sheet switches content by mode instead. tvOS is untouched.
macOS + tvOS typecheck; console UI verified opening Settings in the iPad
simulator with the pair screen wired into the shell.
enricobuehler
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