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>

engine/MUNGA/AUDREND.cpp

@@ -174,6 +174,10 @@ void
 		
 	if (audio_source->IsAudioSourceClipped(GetAudioHead()))
 	{
+		if (getenv("BT_AUDIO_SPATIAL")) { static int s_cl=0; if (s_cl++<40)
+			DEBUG_STREAM << "[spatial] CLIPPED src=" << (void*)audio_source
+				<< " headPos=(" << GetAudioHead()->GetHeadEntity()->localOrigin.linearPosition.x
+				<< "," << GetAudioHead()->GetHeadEntity()->localOrigin.linearPosition.z << ")\n" << std::flush; }
 		//
 		// If it is a transient source then ignore request
 		//
@@ -181,7 +185,7 @@ void
 		{
 			#ifdef LAB_ONLY
 				sourceClippedCount++;
-			#endif		
+			#endif
 			return;
 		}
 		audio_source_priority = audio_source->GetAudioSourcePriority();
@@ -191,6 +195,11 @@ void
 	{
 		audio_source_priority = audio_source->GetAudioSourcePriority();
 		audio_source_volume_scale = audio_source->CalculateSourceVolumeScale();
+		if (getenv("BT_AUDIO_SPATIAL")) { static int s_vs=0; if ((s_vs++ % 120)==0)
+			DEBUG_STREAM << "[spatial] request src=" << (void*)audio_source
+				<< " vol=" << audio_source_volume_scale
+				<< " headPos=(" << GetAudioHead()->GetHeadEntity()->localOrigin.linearPosition.x
+				<< "," << GetAudioHead()->GetHeadEntity()->localOrigin.linearPosition.z << ")\n" << std::flush; }
 	}
 	
 	//
@@ -205,11 +214,19 @@ void
 		audio_source_volume_scale < LowAudioVolumeThreshold
 	)
 	{
+		if (getenv("BT_AUDIO_SPATIAL")) { static int s_dr=0; if (s_dr++<40)
+			DEBUG_STREAM << "[spatial] DROP transient start src=" << (void*)audio_source
+				<< " vol=" << audio_source_volume_scale
+				<< " (below threshold " << LowAudioVolumeThreshold << ")\n" << std::flush; }
 		#ifdef LAB_ONLY
 			sourceClippedCount++;
-		#endif		
+		#endif
 		return;
 	}
+	if (getenv("BT_AUDIO_SPATIAL") && message->controlID == StartAudioControlID) {
+		static int s_st=0; if (s_st++<40)
+			DEBUG_STREAM << "[spatial] START request src=" << (void*)audio_source
+				<< " vol=" << audio_source_volume_scale << "\n" << std::flush; }
 	
 	//
 	//--------------------------------------------------------------------------