Derive Pot's L/Td from the Sud doc instead of a fixed server default

Sud now parses top-level L/Td fields from sude/*.json (defaulting to 0.2/30,
matching the old hardcoded server constants), and derive_plant_params()
returns them alongside M/C - constant for the whole brew, unlike M/C which
vary per step with grain/water mass. All sude/*.json docs gain explicit
L/Td fields.

Callers (tasks/sud.py, SudForecastEstimator, demo_sud.py) switch from the
narrow set_thermal_params(M, C)/set_model_params(M, C) to the full
set_plant_params(params)/set_model_plant_params(params), since
derive_plant_params() now always returns all four keys; both narrow setters
are removed as dead code.

Caught along the way: Pot.set_plant_params() unconditionally rebuilt the
Delay ring buffer, which was harmless when only ever called once at
construction - but now running on every Sud step change, it was wiping
in-flight delayed power at each step boundary. Fixed to only rebuild when
Td actually changes; verified this restores the exact original forecast
result for sud_0010.json.

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

components/plant/pot.py

@@ -42,8 +42,15 @@ class Pot(APlant):
 		# P_loss = L * Mass * (T_plant - T_ambient)
 		self.L = params['L']
 
-		self.Td = params['Td']
-		self.delay = delay.Delay(self.dt, self.Td, 0)
+		# Only rebuilds the delay line if Td actually changed - this now
+		# gets called on every Sud step change (M/C vary with grain/water
+		# mass), not just once at construction, and rebuilding unconditionally
+		# would zero out whatever power was already in flight through the
+		# transport delay at every single step transition.
+		Td = params['Td']
+		if Td != self.Td:
+			self.Td = Td
+			self.delay = delay.Delay(self.dt, self.Td, 0)
 
 	def set_ambient_temperature(self, theta_amb):
 		self.theta_amb = theta_amb
@@ -84,10 +91,6 @@ class Pot(APlant):
 	def is_activated(self):
 		return True
 
-	def set_thermal_params(self, M, C):
-		self.M = M
-		self.C = C
-
 	def set_power(self, power):
 		self.p_in = power