Fix Python 3.10+/websockets compatibility, add CLI args and .gitignore

- ws/message.py, ws/server/ws_server_multi_user.py: drop the loop= kwarg
  and replace asyncio.wait(coroutines) with asyncio.gather(), both of
  which were removed/forbidden in Python 3.10+.
- brewpi/requirements.txt: pin websockets==10.4, the latest version that
  still supports this code's serve()/handler API.
- config.json.sim: move Model to the top level and add the missing gain
  field so it matches the schema brewpi.py and config.json.templ expect.
- brewpi/brewpi.py: add -c/-m/-s/-d CLI args for selecting config/model
  files, simulation mode, and debug.
- .gitignore: exclude __pycache__, logs, the local config.json, and
  editor/venv directories.

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

config.json.sim

@@ -9,14 +9,6 @@
 	"pid_type": "Smith"
 	},
  	"TempCtrl": {
-		"Model": {
-			"theta": 20,
-			"C": 4190,
-			"M": 25,
-			"L": 0.05,
-			"Td": 80,
-			"kn": 0.2
-		},
 		"Kalman": {
 			"var_P"	: 1.0,
 			"var_Q"	: 0.0001,
@@ -35,13 +27,23 @@
 			"kt": 1.5
 		}
 	},
+	"Model": {
+		"theta": 20,
+		"C": 4190,
+		"M": 25,
+		"L": 0.05,
+		"Td": 80,
+		"kn": 0.2,
+		"gain": 0.8
+	},
 	"Plant": {
 		"theta": 20,
 		"C": 4190,
 		"M": 22,
 		"L": 0.05,
 		"Td": 80,
-		"kn": 0.2
+		"kn": 0.2,
+		"gain": 0.8
 	},
 	"Heater": {
 		"port": "/dev/ttyUSB0",