_try_walk_step_assist compared goal surface Y to the capsule centre
(~0.9 m above floor) instead of the actual capsule bottom, disabling
the assist for any surface below ~0.925 m — every terrace we added.
The lift formula used offsets 0.45/0.55 instead of the full capsule
total half-height (CAPSULE_HALF_HEIGHT + PLAYER_CAPSULE_RADIUS = 0.9),
producing zero/negative lift.
Fix: guard uses actual_feet_y = pos.y - CAPSULE_HALF_HEIGHT - PLAYER_CAPSULE_RADIUS;
lift targets goal.y + total_half_height via clampf. Flat floor clicks
and cylinder bumps are unaffected (guard still disabled when goal.y is
at or below true feet level).