Shut heater off on brew end (DONE) and stop (IDLE)

Adds HeaterTask.shutdown() which switches to open-loop at power 0,
disables TC, and broadcasts ClosedLoop=false to clients so the browser
checkbox unchecks immediately. SudTask fires it via a new set_on_end()
callback whenever state reaches DONE or IDLE, giving both a completed
schedule and a manual Stop the same safe behaviour: stirrer and heater
both off, no heater left running unattended.

Re-enabling after shutdown: check the closed-loop checkbox (sends
ClosedLoop=true → TC re-enabled) or adjust the power slider directly;
the next brew's Play press already sends ClosedLoop=true automatically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SH2D4LRuCnhLSzoYerAfJX

tasks/heater.py

@@ -24,6 +24,16 @@ class HeaterTask(ATask):
 	def set_on_closed_loop_changed(self, callback):
 		self._on_closed_loop_changed = callback
 
+	def shutdown(self):
+		"""Called when the brew ends (DONE/IDLE). Switches to open-loop at
+		power 0 and disables TC, mirroring what a Stop press should do."""
+		self.closed_loop = False
+		self.power_soll = 0
+		if self._on_closed_loop_changed:
+			self._on_closed_loop_changed(False)
+		asyncio.create_task(self.send({'ClosedLoop': False}))
+		self.power_set_changed(0)
+
 	def actor(self, y):
 		self.power_actor = max(0, self.device.get_power_max() * y)