Expose xenon reactivity impact on dashboard

src/reactor_sim/neutronics.py

@@ -50,7 +50,7 @@ class NeutronDynamics:
             rod_term
             + temperature_feedback(state.fuel_temperature)
             - fuel_reactivity_penalty(state.burnup)
-            - self._xenon_penalty(state)
+            - self.xenon_penalty(state)
         )
         return rho
 
@@ -96,5 +96,9 @@ class NeutronDynamics:
         decay_Xe = state.xenon_inventory * self.xenon_decay_const
         state.xenon_inventory = max(0.0, state.xenon_inventory + (prod_Xe - decay_Xe - burn_Xe) * dt)
 
+    def xenon_penalty(self, state: CoreState) -> float:
+        """Return delta-rho penalty from xenon inventory (positive magnitude)."""
+        return self._xenon_penalty(state)
+
     def _xenon_penalty(self, state: CoreState) -> float:
         return min(0.03, state.xenon_inventory * self.xenon_reactivity_coeff)