refactor: make ATemperatureSensor's temp observable directly on the sensor

TempSensorSim/TempSensor_max31865's temperature() now stores its
reading on self.temp, so ATemperatureSensor's inherited AttributeChange
(previously never triggered by anything) actually fires. TempSensorTask
no longer keeps its own shadow copy of the reading - it registers its
websocket-push callback on self.sensor directly and just drives the
read each tick; server/brewpi.py's TC-feeding registration moved from
sensor_task to sensor for the same reason.

Priming read happens before registering the callback (not after) since
all tasks are built synchronously at module level, before the asyncio
event loop starts - registering first would fire on_temp_changed's
asyncio.create_task() with no running loop.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GpePKZiEZWbGo9HrfuML6U

components/sensor/tempSensorSim.py

@@ -42,4 +42,5 @@ class TempSensorSim(ATemperatureSensor):
 			innovation = self.stirrer_sigma * np.sqrt(2.0 * alpha) * np.random.normal()
 			self._stirrer_state = (1.0 - alpha) * self._stirrer_state + innovation
 
-		return self.temp_set + self.offset + white + self._stirrer_state
+		self.temp = self.temp_set + self.offset + white + self._stirrer_state
+		return self.temp

components/sensor/tempSensor_max31865.py

@@ -47,7 +47,8 @@ class TempSensor_max31865(ATemperatureSensor):
 
 	def temperature(self):
 		digits = self.read_digits()
-		return self.temp_offset + self.to_temperature(digits)
+		self.temp = self.temp_offset + self.to_temperature(digits)
+		return self.temp
 
 	@staticmethod
 	def to_temperature(digits):