feat: tracer bullet — greybox arena, positioning piloting, auto-fire KINETIC weapon
One-screen 640x360 arena (walls, grid floor, fixed view), mech with
positioning-only movement (WASD/arrows, accel/decel, no aim), auto-fire
KINETIC hardpoint (nearest-target, visible range ring) firing slugs
that damage + knock back, untagged grunt trickle spawner with contact
damage, hull bar HUD, scene-reload on hull zero.
Headless smoke gate: tests/smoke.tscn asserts boot, piloting movement,
spawning, input-free auto-fire, grunt lethality, knockback displacement.
3/3 passes on nh3-dev headless 4.7.1.
vh
380088c694