Add boron reactivity trim and power measurement smoothing

FEATURES.md

@@ -1,7 +1,7 @@
 ## C.O.R.E. feature set
 
 - **Core physics**: point-kinetics with per-bank delayed neutron precursors, temperature feedback, fuel burnup penalty, xenon/iodine buildup with decay and burn-out, and rod-bank worth curves.
-- **Rod control**: three rod banks with weighted worth; auto controller chases 3 GW setpoint with safety backoff; manual mode with staged bank motion and SCRAM; state persists across runs.
+- **Rod control**: three rod banks with weighted worth; auto controller chases 3 GW setpoint with safety backoff and filtered power feedback; manual mode with staged bank motion and SCRAM; state persists across runs. Soluble boron bias contributes slow negative reactivity and trims toward the setpoint.
 - **Coolant & hydraulics**: primary/secondary pumps with head/flow curves, power draw scaling, wear tracking; pressure floors tied to saturation; auxiliary power model with generator auto-start.
 - **Heat transfer**: steam-generator UA·ΔT_lm model with a pinch cap to keep the primary outlet hotter than the secondary, coolant heating uses total fission power with fuel heating decoupled from exchanger draw, and the secondary thermal solver includes passive cool-down plus steam-drum mass/energy balance with latent heat and a shrink/swell-aware feedwater valve controller; dissolved oxygen/sodium drive HX fouling that reduces effective UA.
 - **Pressurizer & inventory**: primary pressurizer trims toward 7 MPa with level tracking, loop inventories/levels steer flow availability, secondary steam boil-off draws down level with auto makeup, and pumps reduce flow/status to `CAV` when NPSH is insufficient.