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>

components/pid/temp_controller_smith.py

@@ -3,7 +3,7 @@ from components.pid.temp_controller_base import TempControllerBase, States
 
 
 class TempController(TempControllerBase):
-	def __init__(self, dt, params, model_params):
+	def __init__(self, dt, params, model_params, theta_amb=20):
 		TempControllerBase.__init__(self, dt, params)
 		self.dt = dt
 		self.last_theta_ist = 20
@@ -11,10 +11,10 @@ class TempController(TempControllerBase):
 
 		# Fast model: same plant model but with zero transport delay, used
 		# to predict the current temperature without the dead time.
-		self.model = Pot(dt, {**model_params, 'Td': 0})
+		self.model = Pot(dt, {**model_params, 'Td': 0}, theta_amb)
 		# Delayed model: keeps the plant's assumed transport delay, so it
 		# can be compared like-for-like against the real (delayed) measurement.
-		self.model_delay = Pot(dt, model_params)
+		self.model_delay = Pot(dt, model_params, theta_amb)
 
 		self.theta_ist_plant = 0
 		self.theta_ist_model = 0