The full-screen panel is fixed inset-0, so it sat on top of the very
list it filters: submitting a query worked, updated the list underneath,
and left the reader staring at an empty panel.
Close it on submit, on picking a contact suggestion, and on clear, so
the results it just produced are what you land on. The header field then
shows the active query rather than the placeholder, so a filtered list
does not look unexplained, and tapping it reopens the panel to refine.
SearchBox gains an autoFocus prop so the panel opens straight to the
keyboard instead of needing a second tap.