vehicles: alien fighter exact through the genuine cross_product2d call

Owner ruling 2026-09-25 narrowly reopens the fighter on new first-party and
link evidence. The hand-written 2D yaw expression becomes cross_product2d
over the two /Od-attested 3D-to-2D views. The body is debug exact, verbatim
in Oct-2001 2276P and matches the Sept-2001 cache.exe map body. The new
SELECT_ANY _cross_product2d now passes the selected-provider link against
actor_combat. +1,088 padded; vehicles 38/39.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

source/units/vehicles.c

@@ -1001,8 +1001,8 @@ static void update_alien_fighter_physics_new(
 				pitch_vectors(&desired_rotation.forward, &desired_rotation.up, sine(definition->unknown364),
 					cosine(definition->unknown364));
 
-			yaw = (desired_rotation.forward.i*vehicle->object.translational_velocity.j-
-				desired_rotation.forward.j*vehicle->object.translational_velocity.i)/
+			yaw = cross_product2d((real_vector2d const *)&desired_rotation.forward,
+				(real_vector2d const *)&vehicle->object.translational_velocity)/
 				definition->unknown2f8*definition->unknown308;
 
 			yaw_vectors(&desired_rotation.up, &desired_rotation.forward, sine(yaw), cosine(yaw));