Wire Pause/Stop to the Sud state machine, with a resumable pause

components/sud.py: adds SudState.PAUSED. pause() freezes RAMPING/
HOLDING (the hold countdown and ramp-reached checks both no-op while
PAUSED, since they're gated on the exact state they froze); start()
now doubles as resume when paused. stop() aborts back to IDLE from
any in-progress state, reusing the same reset logic as __init__/
upload() (factored into _reset_run_state()).

tasks/sud.py: maps 'Pause'/'Stop' messages to the new methods, and
turns the stirrer off on IDLE (not just DONE) so stop() actually
silences it instead of leaving the last step's stirring running.

client/brewpi_gui.py: wires the Pause/Stop toolbar actions, extends
update_sud_actions() so Start doubles as Resume and Stop stays usable
while paused, and freezes the forecast plot's progress line for the
duration of a pause (tracked via accumulated paused time) instead of
letting it drift ahead of actual progress.

components/sud.py

@@ -18,6 +18,7 @@ class SudState(Enum):
 	HOLDING = 2
 	WAIT_USER = 3
 	DONE = 4
+	PAUSED = 5
 
 
 def _merge_defaults(default, override):
@@ -55,11 +56,8 @@ class Sud(AttributeChange):
 		(self.name, self.description, self.schedule,
 			self.pot_mass, self.pot_material) = self._parse_data(data)
 
-		self.index = -1
-		self.hold_remaining = 0.0
-		self.state = SudState.IDLE
-		self.step = None
-		self.user_message = None
+		self._paused_from = None
+		self._reset_run_state()
 
 	@staticmethod
 	def _parse_data(data):
@@ -78,6 +76,16 @@ class Sud(AttributeChange):
 
 		return name, description, schedule, pot_mass, pot_material
 
+	def _reset_run_state(self):
+		"""Resets run-time progress back to a freshly-loaded, not-yet-started
+		IDLE state. Shared by __init__, upload(), and stop()."""
+		self.index = -1
+		self.hold_remaining = 0.0
+		self.state = SudState.IDLE
+		self.step = None
+		self.user_message = None
+		self._paused_from = None
+
 	def download(self):
 		"""Returns the sud.json document currently on disk, for a client to
 		edit and hand back to upload()."""
@@ -100,11 +108,7 @@ class Sud(AttributeChange):
 		with open(self.path, 'w') as f:
 			json.dump(data, f, indent='\t')
 
-		self.index = -1
-		self.hold_remaining = 0.0
-		self.state = SudState.IDLE
-		self.step = None
-		self.user_message = None
+		self._reset_run_state()
 		return True
 
 	def derive_plant_params(self, grain_mass, water_mass):
@@ -125,11 +129,29 @@ class Sud(AttributeChange):
 		}
 
 	def start(self):
+		"""Starts a fresh run from IDLE, or resumes a paused one - whichever
+		applies. No-op otherwise."""
+		if self.state == SudState.PAUSED:
+			self.state = self._paused_from
+			self._paused_from = None
+			return
 		if self.state != SudState.IDLE:
 			return
 		self.index = -1
 		self._advance()
 
+	def pause(self):
+		"""Freezes progress (the hold countdown and ramp-reached checks both
+		no-op while PAUSED) without losing where we are; start() resumes."""
+		if self.state in (SudState.RAMPING, SudState.HOLDING):
+			self._paused_from = self.state
+			self.state = SudState.PAUSED
+
+	def stop(self):
+		"""Aborts the run, discarding progress back to IDLE."""
+		if self.state not in (SudState.IDLE, SudState.DONE):
+			self._reset_run_state()
+
 	def confirm(self):
 		if self.state == SudState.WAIT_USER:
 			self._advance()