Add Closed-loop/Open-loop heater control mode

Closed-loop (default, checkbox checked): TC has exclusive control over
the heater; temp-soll and heatrate-soll sliders are active; direct
heater power entry is disabled. TC now stays enabled at server startup
and whenever closed-loop mode is active — SudTask no longer disables it
on IDLE/DONE, so adjusting temp-soll manually with no sud running
immediately drives the heater via the TC.

Open-loop (checkbox unchecked, only selectable when paused/stopped):
TC is disconnected from the heater; only the heater-power slider is
active. Switching back to closed-loop resets power_soll to 0 and
re-enables the TC.

On play, the mode is automatically reset to closed-loop.

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

tasks/sud.py

@@ -220,14 +220,6 @@ class SudTask(ATask):
 		if value in (SudState.DONE, SudState.IDLE):
 			self.stirrer.set_duty_cycle(1.0)
 			self.stirrer.set_speed(0)
-			# A finished/stopped run no longer owns the controller - hand
-			# control back to manual mode (off by default there too).
-			self.tc.set_enabled(False)
-		else:
-			# Any other state (RAMPING/HOLDING/WAIT_USER/PAUSED) means a
-			# run is in progress and needs the controller actively driving
-			# the heater.
-			self.tc.set_enabled(True)
 
 	def on_user_message_changed(self, value):
 		asyncio.create_task(self.send({'UserMessage': value}))