Expo SDK upgrade

Moves the app (every app and shared package, when multi-package) to the next Expo SDK, or the build toolchain to another Xcode or Android level, in one proven step: only when the new SDK is stable and old enough or a store deadline forces it, with every package, tool, override, code migration and toolchain change in one commit, and two checkers that prove when a move is due and that the repo sits on one SDK line.

Rules that must hold