Make ambient temperature configurable and wire it everywhere it was hardcoded

brewpi.py passed a literal 20 as theta_amb to Pot, and
temp_controller_smith.py's two internal Pot models (and every demo's
Pot/TempController instantiation) silently relied on Pot's default of
20 instead. Add a top-level ambient_temperature key to
config.json(.templ/.sim), thread it through brewpi.py into both the
real plant and the Smith predictor's models via a new theta_amb param
on TempController, and make the demos pass it explicitly too.

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

brewpi/brewpi.py

@@ -29,6 +29,7 @@ if __name__ == '__main__':
 	DT = config['Controller']['dt']
 	DT_TASK = 1.0 / config['Controller']['sim_warp_factor']
 	DT_TASK_TRACER = DT_TASK / DT
+	theta_amb = config['ambient_temperature']
 
 	# Sensor
 	sensor = TempSensorFactory.create(config['Controller']['sensor_name'], temp_offset=-0.15, variance=0.01)
@@ -37,7 +38,7 @@ if __name__ == '__main__':
 
 	# Plant
 	pot_params = config['Plant']
-	pot = Pot(DT, pot_params, 20)
+	pot = Pot(DT, pot_params, theta_amb)
 	taskmgr.add(PotTask(pot, DT_TASK, dispatcher.msgio_get("Pot")))
 
 	# Heater
@@ -47,7 +48,7 @@ if __name__ == '__main__':
 	taskmgr.add(heater_task)
 
 	# Temperature Controller
-	tc = PidFactory.create(config['Controller']['pid_type'], DT, config['TempCtrl'], config['Model'])
+	tc = PidFactory.create(config['Controller']['pid_type'], DT, config['TempCtrl'], config['Model'], theta_amb=theta_amb)
 	tc_task = TcTask(tc, DT_TASK, dispatcher.msgio_get("TempCtrl"))
 	taskmgr.add(tc_task)