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/sud_forecast.py

@@ -89,9 +89,9 @@ class SudForecastEstimator:
 			if step is None:
 				return
 			params = sud.derive_plant_params(step.get('grain_mass', 0), step.get('water_mass', 0))
-			pot.set_thermal_params(params['M'], params['C'])
-			if hasattr(tc, 'set_model_params'):
-				tc.set_model_params(params['M'], params['C'])
+			pot.set_plant_params(params)
+			if hasattr(tc, 'set_model_plant_params'):
+				tc.set_model_plant_params(params)
 			if sud.state == SudState.RAMPING and step['temperature'] is not None:
 				tc.set_theta_soll(step['temperature'])
 				tc.set_heatrate_soll(step['ramp']['rate'])