Add turbine throttle mapping and back-pressure penalty

src/reactor_sim/reactor.py

@@ -461,6 +461,10 @@ class Reactor:
                 break
             turbine_state = state.turbines[idx]
             if idx in active_indices:
+                # Simple throttle map: reduce throttle when electrical demand is low, open as demand rises.
+                demand = turbine_state.load_demand_mw
+                throttle = 0.4 if demand <= 0 else min(1.0, 0.4 + demand / max(1e-6, turbine.rated_output_mw))
+                turbine.throttle = throttle
                 turbine.step(state.secondary_loop, turbine_state, steam_power_mw=power_per_unit, dt=dt)
                 if power_per_unit <= 0.0 and turbine_state.electrical_output_mw < 0.1:
                     turbine_state.status = "OFF"