perf(ship): reuse member ShipAction instead of allocating per tick

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.

TODO.md

@@ -14,13 +14,7 @@ The training pipeline is built — see `TRAINING.md` (self-play PPO via the vend
 
 Bugs found in an adversarial review. None are gameplay- or physics-affecting, so all are safe to land against the current `Game/bots/` checkpoints.
 
-- [x] `VideoSettings.apply_to_environment()` (`scripts/video_settings.gd`) compounds on every arena load: `env.glow_intensity *= glow_scale` mutates an `Environment` that is a `[sub_resource]` of the arena scene, and Godot shares sub-resources across instantiations of a cached `PackedScene`. Glow at 50% becomes 25% then 12.5% across repeat entries. Fix by duplicating the Environment in `Arena._ready()` (`scripts/arena.gd`). Regression test: set glow to 50%, enter/leave Free Play three times, confirm it's still 50%.
-- [x] Collapse the four disagreeing team palettes into one source of truth — `ship.gd`, `HUDController.gd` and `goal.gd` each declare `TEAM_COLORS`, `arena_boundary.gd` exports `team0_tint`/`team1_tint`, and `arena_deck.gdshader` defaults to a fifth pair. Three of them disagree, so nose, goal rim, end zone and scoreboard are all different blues.
 - [ ] Goal scoring volume (3.5 x 1.5, `objects/goal.tscn`) is smaller than the drawn mouth (3.7 x 1.65, `ArenaBoundary.GOAL_APERTURE_*`) — a ball crossing the visible edge doesn't score. Derive the aperture constants from the goal's collision shape, the way `goal.gd:53` already measures its own visuals.
-- [x] `match_mode.gd`: full time can fire mid-kickoff-countdown, and the stalled coroutine resumes into the dying scene (can re-emit `kickoff_countdown` / unfreeze bodies for a frame). Guard `_run_kickoff_countdown` with a match-over flag.
-- [x] `match_mode.gd` emits `timer_updated` every frame for a value that changes once a second; the HUD re-formats and re-shapes the label each time. Emit only on change, matching `ship.gd`'s threshold-gated telemetry discipline.
-- [x] `HUDController` binds to `get_first_node_in_group("ship")` in a group that always has 2+ members — works only because the player ship happens to spawn first. Have the game mode hand the HUD its target ship.
-- [ ] Reuse a member `ShipAction` in `ship.gd` (controllerless path) and `player_ship_controller.gd` instead of allocating one per physics tick; `ai_ship_controller.gd` already does this correctly.
 - [ ] Delete the duplicate 1 MB texture — `assets/textures/planet_surface.png` and `assets/models/nebula_planet_planet_surface.png` are byte-identical.
 
 ## Performance