feat(errand): no move limit — ends only on reaching the house (analysis) or zero health

merge: errand_runner scenario (visual-only city errand + find-your-body discovery)

feat(engine): health/damage + interact action + on_step_effects/check_success in turn loop

docs(engine): document check_success in MotiveGridGame turn-loop + survived docstring

feat(engine): additive Scenario.check_success early-win hook (default False)

feat(engine): per-scenario turn_order with predator-first step swap

docs: refresh engine README for proteus/game/engine relocation

refactor: restructure proteus into game/web subpackages