#124 twist-sign VERIFIED correct (live missile bench) + the rig to do it

The frame-adapter's inferred twist-sign flip (SelectSlice theta -= twist,
vs the binary's += pre-reflection) was the last unverified half of #124 --
every earlier probe ran at twist 0.  Bench: stationary madcat target with
the torso PINNED at 0 / +140 / -140 deg, LRM salvos from a fixed shooter
(missiles = the authentic cylinder path; the binary DROPPED zone -1 beam
damage).  Result: slice picks track the physically-facing flank in BOTH
directions (twist-left -> right-family zones for left-flank impacts,
twist-right -> left-family), deterministic, wrong-sign outcome (slice 7
vs observed slice 1) clearly excluded.  No game-code change needed.

Instrumentation added (all env-gated):
- torso.cpp BT_FORCE_TWIST=<-1..1>: HOLD the sim's analogTwistAxis (the
  input-level pin was dead -- live input rides the CONTROLS.MAP device
  push, and Basic mode auto-centers; sim-level is plumbing-independent).
- dmgtable.cpp [slice] line: rot flag, live twist, thetaIn/thetaAdj,
  chosen slice -- the weighted leaf roll made zone-only logs ambiguous.
- [dmgresolve] now names the zone (BTMechZoneSegAndName).
- mech4.cpp BT_FORCE_TWIST input pin + one-shot mode cycle (kept as doc
  of the dead path), mechmppr [mppr] mode probe.
- scratchpad/night11/twistsign.sh: the 3-config bench.

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

game/reconstructed/mechmppr.cpp

@@ -840,6 +840,15 @@ void
 					extern float gBTElevAxis;
 					stickPosition.y = gBTElevAxis;
 				}
+				// #124 twist-sign bench probe: is the axis routed, and in what mode?
+				if (getenv("BT_TORSO_LOG"))
+				{
+					static int s_mp = 0;
+					if ((s_mp++ % 60) == 0 && s_mp < 1200)
+						DEBUG_STREAM << "[mppr] mode=" << (int)controlMode
+							<< " twistAxis=" << gBTTwistAxis
+							<< " keyTurn=" << key_turn << "\n" << std::flush;
+				}
 				if (controlMode == BasicMode)
 				{
 					stickPosition.x = key_turn;