Simplify Pot: drop gain/theta params, seed initial temp from ambient

[Pot] - removed the gain (efficiency) factor and the separate
"theta" initial-temperature param; Pot now starts at theta_amb and
set_power()/get_power() operate on p_in directly. Added
set_ambient_temperature() for live ambient updates. Dropped the
now-unused "theta"/"gain" keys from Model/Plant in config.json.sim
and config.json.templ (also fixes a JSON syntax error in
config.json.templ: trailing commas left over after removing "gain"
made Model/Plant fail to parse).
[Sensor] - fix missing space in TempSensorSim.temperature()'s
offset/variance expression (cosmetic, no behavior change).

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

config.json.templ

@@ -11,11 +11,6 @@
 	"pid_type": "Smith"
 	},
  	"TempCtrl": {
-		"Kalman": {
-			"var_P"	: 1.0,
-			"var_Q"	: 0.0001,
-			"var_R"	: 1.0
-		},
 		"Hold": {
 			"kp": 0.4,
 			"ki": 0.0,
@@ -38,22 +33,16 @@
 		}
 	},
 	"Model": {
-		"theta": 20,
 		"C": 4190,
 		"M": 25,
 		"L": 0.05,
-		"Td": 15,
-		"kn": 0.2,
-		"gain" : 0.8
+		"Td": 15
 	},
 	"Plant": {
-		"theta": 20,
 		"C": 4190,
 		"M": 25,
 		"L": 0.05,
-		"Td": 15,
-		"kn": 0.2,
-		"gain" : 0.8
+		"Td": 15
 	},
 	"Heater": {
 		"port": "/dev/ttyUSB0",