Audio: restore the dropped ExecuteWatchers poll -- polled audio watchers were ALL dead (task #50)

User: "when I start moving all the sounds fade away, no footsteps."  Diagnosis
chain (all empirical, BT_AUDIO_SPATIAL/BT_ATTRBIND_LOG traces):
- The audio head DOES track the mech (listener-relative positioning verified
  while driving) -- not a spatial bug.
- The idle sounds correctly STOP on leaving the standing state; the MOVING
  sounds never started because every POLLED audio watcher was dead:
  the reconstructed Mech::PerformAndWatch replaced the engine performance but
  dropped the ExecuteWatchers() step from the engine tail (Simulation::
  PerformAndWatch = Perform -> ExecuteWatchers -> WriteSimulationUpdate).
  Only PUSHED StateIndicator watchers (SetState->Execute) ever fired -- which
  is exactly why state sounds worked but footsteps/motion-scaled audio didn't.
  FIX: poll ExecuteWatchers() (AreWatchersDelayed-gated) before the update
  write.  Immediately unlocks the polled family: MissileLoaded01/LaserLoaded01
  ready dings, ProgramButton01, motion scales (PlayNote 15 -> 30 per run).

- FootStep (0x1e) backed REAL: was the inert attrPad (an AudioLogicalTrigger
  polls it -- threshold-crossing pulse per foot plant).  New footStep member,
  pulsed by SetBodyAnimation on entering any locomotion clip 1..0x17 (runtime
  stride alternation MEASURED as body states 12<->13 -- the enum-name numbering
  does not match runtime clip ids), decayed by IntegrateMotion (~1/3 s).
- Footstep volume is speed-scaled (AudioMotionScale on LocalVelocity): at
  standstill the transient start computes volume 0 and the renderer drops it
  (LowAudioVolumeThreshold) -- so footfalls are audible at real walking speed.

Diagnostics kept (BT_AUDIO_SPATIAL): spatial dist/vol per source, CLIPPED/DROP/
START at the request gate, vol=0 factor breakdown, scale->0 sends, trigger
notifications, watcher poll-rate probe.

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

game/reconstructed/mech.cpp

@@ -711,7 +711,7 @@ const Mech::IndexEntry
 	ATTRIBUTE_ENTRY(Mech, MaxRunSpeed,             reverseStrideLength),	// 0x1b (existing @0x34c = run/top speed)
 	ATTRIBUTE_ENTRY(Mech, EyepointRotation,        eyepointRotation),		// 0x1c (real member -- the eye reads it per frame)
 	ATTRIBUTE_ENTRY(Mech, TargetReticle,           targetReticle),		// 0x1d (real Reticle struct -- task #36)
-	ATTRIBUTE_ENTRY(Mech, FootStep,                attrPad),				// 0x1e
+	ATTRIBUTE_ENTRY(Mech, FootStep,                footStep),				// 0x1e real pulse (AudioLogicalTrigger; one rising edge per foot plant)
 	ATTRIBUTE_ENTRY(Mech, AnimationState,          animationState),			// 0x1f real StateIndicator (audio state-watcher binds + AddAudioWatcher)
 	ATTRIBUTE_ENTRY(Mech, ReplicantAnimationState, replicantAnimationState),	// 0x20 real StateIndicator
 	ATTRIBUTE_ENTRY(Mech, LinearSpeed,             linearSpeed),			// 0x21 (live forward speed)
@@ -923,6 +923,8 @@ Mech::Mech(
 	collisionState          = StateIndicator(4);	// CollisionStateCount
 	collisionState.SetState(0);						// NoCollisionState
 	collisionTemporaryState = 0;
+	footStep                = 0;					// FootStep pulse (audio trigger)
+	footStepDecay           = 0;
 	radarRange          = 1000.0f;						// radar display scale (SetTargetRange is stubbed;
 														// 1km default zoom so contacts within ~500m show on
 														// the radar, vs the config maximum_range=4000 edge)