App wiring: Repose platform runners + sim/gamepad helpers.
A game provides a root view; [ShellHooks] is the game-side per-frame
contract (snapshot production + variable-rate hook) that the game's own
root closure drives. The run_* runners below are thin mounts only:
they do not call ShellHooks or step the sim — stepping stays game-side
via [Sim::step] (see the rozvp pilot runner for the reference wiring).
Per-game UI stays in the game crate as Repose views.