MP: peer true-mirror cadence -- drive the body clip from actual replicated motion (task #50)

Toward a truer mirror (user: peer 'hesitates/skips on accel/decel, master has
smoother transitions').  The body channel FOLLOWS the master's replicated STATE
(96a896a) but its CADENCE (bodyCycleSpeed) is still slewed LOCALLY toward the
replicated commanded speed -- which drifts from the master's actual cadence, so
the animation phase wanders until a record snaps it (the hesitation).

FIX (replicant-gated, single-player untouched): peerMirrorSpeed member = the
actual replicated ground speed (|updateVelocity|, set in the peer branch); the
body channel walk (6/7) + reverse (0xc/0xd) cases override bodyCycleSpeed with
it (clamped to the state's band) right before the clip advance, so the peer's
clip advances at the master's REAL rate instead of a locally-drifting slew.
peerMirrorSpeed = -1 on the master/single-player -> the authentic slew runs.
BT_NO_MIRROR_CAD / BT_PEER_LEGCH revert.

Verified autonomous (through-zero sweep): no crash, body channel advances forward
(back-steps ~0), feet track (position ratio 1.05, maxStep 1.68u).  Perceived
smoothness is the visual test (harness saturates).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

game/reconstructed/mech.cpp

@@ -916,6 +916,7 @@ Mech::Mech(
 	poseSyncLatch = 0;									// @0x77c (was absorbed Wword(0x1df))
 	heatLevelSnapshot = 0;								// @0x780 (type-7 deadband baseline)
 	mirrorBodyAdv  = 0.0f;								// master send-mirror gait travel
+	peerMirrorSpeed = -1.0f;							// peer true-mirror cadence (disabled by default)
 	angMirrorYaw   = 0.0f;								// scalar peer-yaw mirror (port addition)
 	angMirrorRate  = 0.0f;
 	angMirrorValid = 0;