refactor: replace plant_name with per-component type keys in config

PlantFactory.create() no longer takes plant_name; sim vs real is derived
from Heater.type. StirrerFactory is wired from Stirrer.type. HeaterFactory
registry key lowercased to "hendi" to match config. Controller.plant_name
removed from both config templates.

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

config-sim.json.tpl

@@ -1,7 +1,6 @@
 {
 	"ambient_temperature": 20,
 	"Controller" : {
-	"plant_name": "sim",
 	"pid_type": "Smith"
 	},
  	"TempCtrl": {
@@ -34,12 +33,10 @@
 		}
 	},
 	"Heater": {
-		"port": "/dev/ttyUSB0",
-		"speed": "115200"
+		"type": "sim"
 	},
 	"Stirrer": {
-		"port": "/dev/ttyACM0",
-		"speed": "115200"
+		"type": "sim"
 	},
 	"TempSensor": {
 		"type": "sim",