Force the heater off and show a "Cool down" indicator during a passive cooldown

A ramp step whose target is below the current actual temperature can
only be reached by ambient cooling - the heater can't actively cool.
SudTask now detects this once per ramp phase and calls the controller's
new set_cooling() override (forces y=0, bypassing the FSM) instead of
waiting for its hysteresis-based IDLE transition. The GUI shows a
blinking blue "Cool down" label in the status bar while this is active.
Progression already only advances once theta_ist matches theta_soll
regardless of direction, so no change was needed there.

client/brewpi_gui.py

@@ -227,6 +227,18 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.status_label_env = QtWidgets.QLabel()
 		self.statusBar().addPermanentWidget(self.status_label_env)
 		self.update_status_env_label()
+
+		# Blinking indicator for a Sud ramp step that's cooling down
+		# (target below the current temperature - the heater is forced off
+		# server-side and we just wait for ambient loss to catch up).
+		self.sud_cooling = False
+		self.status_label_cooling = QtWidgets.QLabel("Cool down")
+		self.status_label_cooling.setStyleSheet("color: blue; font-weight: bold;")
+		self.status_label_cooling.setVisible(False)
+		self.statusBar().addPermanentWidget(self.status_label_cooling)
+		self.cooling_blink_timer = QtCore.QTimer(self)
+		self.cooling_blink_timer.timeout.connect(self.on_cooling_blink)
+
 		self.update_sud_actions()
 		self.btn_connect.clicked.connect(self.on_btn_connect_clicked)
 		self.actionStart.triggered.connect(self.on_action_sud_start)
@@ -336,6 +348,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			self.sud_start_time = None
 			self.sud_paused_total = 0.0
 			self.sud_pause_started_at = None
+			self.set_sud_cooling(False)
 			self.update_sud_actions()
 			self.update_status_env_label()
 
@@ -361,6 +374,20 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		ambient = "{:.1f}°C".format(self.ambient_temp) if self.ambient_temp is not None else "-"
 		self.status_label_env.setText("Ambient: {}   Warp: {:.1f}x".format(ambient, self.warp_factor))
 
+	def set_sud_cooling(self, cooling):
+		if cooling == self.sud_cooling:
+			return
+		self.sud_cooling = cooling
+		if cooling:
+			self.status_label_cooling.setVisible(True)
+			self.cooling_blink_timer.start(500)
+		else:
+			self.cooling_blink_timer.stop()
+			self.status_label_cooling.setVisible(False)
+
+	def on_cooling_blink(self):
+		self.status_label_cooling.setVisible(not self.status_label_cooling.isVisible())
+
 	def on_slider_temp_soll_changed(self, value):
 		print("on_slider_temp_soll_changed {}".format(value))
 		self.msg_tempctrl.send({'Soll': {'Temp': value}})
@@ -544,6 +571,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 					self.statusBar().showMessage("Step {}: {}".format(step.get('Index'), descr))
 				else:
 					self.statusBar().clearMessage()
+				self.set_sud_cooling(step.get('Cooling', False))
 		self.update_sud_actions()
 
 	def update_sud_forecast(self, doc):