refactor: drop firmware-version display, move Enable toggle to Controller

Firmware version is already printed to the log at connect() time
(HendiCtrl/Pololu1376) - remove the live GUI/websocket firmware
reporting entirely (Connectable, HeaterHendi/StirrerPololu1376,
Heater/StirrerTask, web GUI) as redundant.

Also move the Heater panel's Closed-loop checkbox into the Controller
panel and rename it "Enable" - the Controller panel now shows a
live Enabled (green) / Disabled (gray) status badge next to its
heading, matching the Connected/Disconnected badges on the Heater/
Stirrer panels.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YaPLuRPpyjWcwhMvCvpHCL

tasks/stirrer.py

@@ -16,7 +16,6 @@ class StirrerTask(ATask):
 		stirrer_device.set_on_changed("dutyCycle", self.on_dutycycle_changed)
 		stirrer_device.set_on_changed("cycleTime", self.on_cycletime_changed)
 		stirrer_device.set_on_changed("connected", self.on_connected_changed)
-		stirrer_device.set_on_changed("firmware_version", self.on_firmware_version_changed)
 
 	def on_speed_changed(self, value):
 		asyncio.create_task(self.send({'Speed': value}))
@@ -38,9 +37,6 @@ class StirrerTask(ATask):
 		if self._on_connected_changed:
 			self._on_connected_changed(value)
 
-	def on_firmware_version_changed(self, value):
-		fire_and_forget(self.send({'FirmwareVersion': value}))
-
 	async def recv(self, data):
 		for pair in data.items():
 			if pair[0] == 'Connect':
@@ -69,7 +65,6 @@ class StirrerTask(ATask):
 		# for why a simulated device's connect() alone doesn't fire the
 		# observer.
 		await self.send({'Connected': self.device.connected})
-		await self.send({'FirmwareVersion': self.device.firmware_version})
 
 		with self.device.open():
 			while True: