show threat rate in debug output

src/lib/sim/WaveSystem.h

@@ -36,6 +36,11 @@ public:
 
     double threatLevel() const;
 
+    // Current rate at which threatLevel() is increasing, in threat/second
+    // (REQ-WAV-THREAT-RATE). 0 during a quiet window (REQ-WAV-QUIET) or when
+    // the rate formula evaluates to a negative value.
+    double threatAccumulationRate() const;
+
     // Current enemy-station generation level (0 for initial set,
     // incremented by 1 after each push — REQ-PSH-STATION-STATS).
     int generation() const;