sensor: model real temp sensor noise in TempSensorSim

Replaces the opaque variance/√12 formula with two explicit noise components:

  sigma (default 0.05 °C) — white Gaussian noise, calibrated against the
  20260628T184903 Sud-0010 log (detrended hold-phase tick-to-tick std ≈ 0.053 °C).

  stirrer_sigma / stirrer_tau — optional AR(1) low-frequency component for
  stirrer-induced fluctuations (off by default); steady-state std equals
  stirrer_sigma, correlation time equals stirrer_tau ticks.

plant_factory.py updated to use sigma=0.05 instead of the old variance=0.01
(which gave std ≈ 0.003 °C — far too quiet).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/plant/plant_factory.py

@@ -21,7 +21,7 @@ class PlantFactory:
 		if "sim" in plant_name:
 			heater = HeaterFactory.create("sim", heater_config)
 			pot = Pot(dt)
-			sensor = TempSensorFactory.create("sim", temp_offset=-0.15, variance=0.01)
+			sensor = TempSensorFactory.create("sim", temp_offset=-0.15, sigma=0.05)
 			return heater, pot, sensor
 
 		heater = HeaterFactory.create("Hendi", heater_config)