Fix torso-pitch aim ray: gyro-stabilized boresight from the mech torso

The aim/pick ray was the active RENDER EYE's view direction, which made a
mech unable to aim at a distant enemy:
  (a) it inherited the mech BODY pitch -- on a slope the body tilts ~8 deg to
      conform to terrain, so the boresight pointed that far DOWN and the pick
      ray hit the ground ~50-100m short of the target (groundPicks, never
      mechPicks); and
  (b) in CHASE view (the default) it was the elevated behind-the-shoulder
      camera, so the ray started over the mech's shoulder and flew high.

Fix (L4VIDRND DPLEyeRenderable::Execute, the BTSetAimCamera publish):
- LEVEL the boresight: drop the view-direction pitch and rebuild an upright
  basis (world +Y up) -- the guns fire along the mech's gyro-stabilized
  HORIZONTAL heading, not the terrain-pitched body.  Reticle X still carries
  the torso twist (BTTwistToReticleX); reticle Y any elevation.
- ANCHOR the ray origin at the mech's TORSO (myEntity->localToWorld
  translation + ~5) instead of the render eye, so it is correct in BOTH the
  chase (default) and cockpit views.

Verified end-to-end: solo, enemy 120m ahead, BOTH chase and cockpit view ->
[target] "MECH under boresight ... mechPicks=59 groundPicks=0" -> beam ->
*** DESTROYED.  Also proved PickRayHit resolves a REPLICANT when aimed at it
(hit=1 at 757m, 2-node run).

mech4: BT_GOTO="enemy" test aid now chases the nearest peer of ANY instance
(solo dummy OR replicant), not just replicants.

Still open (locomotion, not aim/MP): BT_GOTO/BT_AUTODRIVE stall short of the
enemy, so an AUTOMATED 2-node kill via the real beam isn't demonstrated yet
(the FORCE_DMG hook still is).  A human can now aim correctly in the default
view.  Solo un-regressed; build clean; KB validator clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

game/reconstructed/mech4.cpp

@@ -1515,8 +1515,7 @@ void
 					for (int ei = 0; ei < enc; ++ei)
 					{
 						Mech *em = (Mech *)ec[ei];
-						if (em == 0 || em->GetInstance() != ReplicantInstance
-							|| em->IsMechDestroyed()) continue;
+						if (em == 0 || em->IsMechDestroyed()) continue;	// any peer (solo dummy OR replicant)
 						Point3D ep = em->localOrigin.linearPosition;
 						float edx = (float)ep.x - (float)localOrigin.linearPosition.x;
 						float edz = (float)ep.z - (float)localOrigin.linearPosition.z;