Clean up after Smith predictor rewrite and drop unused/stale config

[brewpi] - drop trace vars for the dtheta_ist_* attributes removed
when temp_controller_smith.py dropped Kalman filtering
[Pot] - drop unused kn field (never read since the noise-injection
code that used it was dropped)
[GUI] - default WS connection to ws://localhost:8765

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

components/plant/pot.py

@@ -27,9 +27,6 @@ class Pot(APlant):
 		# Energy transport propagation delay
 		self.Td = params['Td']
 
-		# TBD
-		self.kn = params['kn']
-
 		# Plant temperature [°C]
 		self.temp = params['theta']