Pot: require plant params and ambient temperature via setters, not the constructor

Pot.__init__ now only takes dt; set_plant_params() and set_ambient_temperature()
must be called before process(), which now raises RuntimeError if either is
missing instead of silently computing on whatever the constructor happened to
default to. set_ambient_temperature() only seeds the plant's starting
temperature the first time it's called, so changing ambient mid-run still
can't clobber an in-progress simulated temperature. Updates all callers
(server/brewpi.py, TempController(Smith)'s two internal models,
SudForecastEstimator, and the plant/pid/sud demo scripts) to call the setters
right after construction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DkkuG48uHFCGKe6dPSERFk

server/brewpi.py

@@ -76,7 +76,9 @@ if __name__ == '__main__':
 	taskmgr.add(sensor_task)
 
 	# Plant
-	pot = Pot(DT, DEFAULT_PLANT_PARAMS, theta_amb)
+	pot = Pot(DT)
+	pot.set_plant_params(DEFAULT_PLANT_PARAMS)
+	pot.set_ambient_temperature(theta_amb)
 	taskmgr.add(PotTask(pot, DT_TASK, dispatcher.msgio_get("Pot")))
 
 	# Heater