MP combat step 1 (target any peer) DONE; step 2 (cross-pod damage) localised (task #46)

STEP 1 -- target any peer mech: DONE + verified. A live-mech registry
(BTRegisterMech/BTDeregisterMech from the Mech ctor/dtor) collects
every mech -- player, dummy, and peer replicants. The boresight
world-pick walks BTGetTargetCandidates (all mechs != shooter, closest
ray hit) and the whole fire/damage block retargets from the solo
gEnemyMech to the picked hotTarget; missile/projectile validation
generalised via BTIsRegisteredMech. Verified one-box: instance A
enumerates B's mech as a live ReplicantInstance (20 zones, ownerID=3).
Solo un-regressed (pick->damage->kill clean, 28 hits + DESTROYED).

STEP 2 -- cross-pod damage: dispatch + engine reroute are CORRECT and
invoked with a valid owner, but the dispatched message doesn't reach
the master. Entity::Dispatch (ENTITY.cpp:244) reroutes a replicant's
msg via application->SendMessage(ownerID,...); BT_MP_FORCE_DMG proves A
dispatches at B's replicant with ownerID=3, yet B takes 0 STEP-6
damage. Corrects the KB's [T3] "Dispatch already reroutes": the reroute
FIRES; the break is downstream in the transport/delivery of a
dispatched entity-message (update records flow fine -- net-rx works).
Next MP task = that wire delivery. Diagnostics BT_MP_LOG /
BT_MP_FORCE_DMG retained.

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

game/reconstructed/mech.cpp

@@ -729,6 +729,13 @@ Mech::Mech(
 	*(Scalar *)((char *)this + 0x384) = 0.0f;
 	*(int    *)((char *)this + 0x38c) = -1;				// targeted sub-zone
 
+	// LIVE-MECH REGISTRY (task #46, MP targeting): every Mech -- player, the
+	// solo dummy, AND every peer replicant -- registers here so the boresight
+	// world-pick can test ALL of them, not just the solo gEnemyMech.  The dtor
+	// deregisters (rare -- wrecks stay; replicants drop when a peer leaves).
+	extern void BTRegisterMech(Entity *m);
+	BTRegisterMech((Entity *)this);
+
 	//
 	// Install the Mech vtable and construct the embedded member objects.
 	//
@@ -1479,6 +1486,9 @@ Mech::~Mech()
 {
 	Check(this);
 
+	extern void BTDeregisterMech(Entity *m);		// task #46 live-mech registry
+	BTDeregisterMech((Entity *)this);
+
 	vtable = &PTR_FUN_0050cfa8;
 
 	// Teardown-health probe (env-gated): collisionLists@0x2e4 must be LIVE at ~Mech