Audio: footstep-chain diagnostics -- every link verified except the final trigger fire (task #50)

Instrumentation (all BT_AUDIO_LOG/BT_AUDIO_SPATIAL-gated): mech watcher-poll
probe (delayed flag + socket count via new Simulation::DebugAudioWatcherCount),
per-sim audio-socket size in ExecuteWatchers, trigger notifications (val>0),
watcher poll-rate/change probes, footstep pulse address trace.

VERIFIED working: FootStep binds to the real member (pulse addr == bound ptr,
same run); pulses fire per stride (40/run); the watcher registers on the mech
(audioWatchers=20 after audio-object creation); the mech's poll runs
(delayed=0, simFlags=0x1110); Logical == int (STYLE.H:132) matches the member
type.  The idle<->moving engine crossfade (AudioMotionScale on LocalVelocity
through the restored watcher poll) is CONFIRMED audible in play.

REMAINING: the FootFall transient still doesn't reach SetupPatch -- next probe
is the trigger's streamed threshold/inverse config and the speed-scaled
transient volume at the renderer drop gate (LowAudioVolumeThreshold=0.3).

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

game/reconstructed/mech4.cpp

@@ -5205,6 +5205,10 @@ void
 	// (AudioLogicalTrigger FootStep, AudioMotionScale/Trigger LocalVelocity, ...)
 	// never executed -- only the PUSHED StateIndicator watchers fired.  That's
 	// why footsteps/motion-scaled sounds were silent while state sounds worked.  [T0]
+	if (getenv("BT_AUDIO_LOG")) { static int s_wd=0; if ((s_wd++ % 300)==0)
+		DEBUG_STREAM << "[audio] mech watcher poll: delayed=" << (int)AreWatchersDelayed() << " audioWatchers=" << DebugAudioWatcherCount()
+			<< " simFlags=0x" << std::hex << (unsigned)simulationFlags << std::dec
+			<< "\n" << std::flush; }
 	if (!AreWatchersDelayed())
 		ExecuteWatchers();