ship.gd's controllerless path and player_ship_controller.gd each
allocated a fresh ShipAction every physics tick; ai_ship_controller.gd
and rl_ship_controller.gd already avoid this via a persistent member.
Convert both to reuse a member instance, matching the existing
full-field-overwrite convention (rather than +=/-= off a fresh zero).
Also drop the completed items from TODO.md.