fix(ios): hand-built safe-area inset (env() returns 0 on iOS Safari + standalone)
env(safe-area-inset-top) resolves to 0 on this iOS in both Safari and the installed PWA
(content under the camera). A boot script measures the inset directly and, if it comes
back empty on a notch/Dynamic-Island iPhone (logical height >= 812), falls back to a fixed
50px. The masthead padding reads --ios-safe-top. CSS buster -> v54.