Switch the motors off when the designs are done or stopped

After the last design (or a Stop), the player sends $SLP (GRBL and FluidNC
sleep), so the motors stop holding and the table is quiet. The page shows
"Motors off"; the next design wakes the controller (reset + unlock) and homes
first, since the arm can be moved by hand while the motors are off. The jog
panel wakes it too. Setting: motion.motors_off_when_done (default true).

Checked on the real Uno: Idle -> $SLP -> Sleep -> reset -> Alarm -> $X -> Idle.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

software/tests/fakegrbl.py

@@ -34,6 +34,7 @@ class FakeGrbl:
         self.hold = False
         self.alarm = False
         self.unplugged = False       # set to pretend the USB cable came out
+        self.sleeping = False        # after $SLP: motors off until a reset
         self.absolute = True
         self.settings = {'$3': '0', '$100': '250.000', '$101': '250.000', '$110': '500', '$111': '500'}
         self.max_rx = 0
@@ -80,6 +81,8 @@ class FakeGrbl:
                     self.hold = False
                 elif b == 0x18:
                     moving = bool(self.planner) and not self.hold
+                    if self.sleeping:                     # waking from sleep: GRBL comes up locked
+                        self.sleeping, self.alarm = False, True
                     if moving:
                         self.alarm = True
                         self._emit('ALARM:3')            # reset while in motion: position lost
@@ -124,7 +127,7 @@ class FakeGrbl:
                    f'{self.wco[0]:.3f},{self.wco[1]:.3f},0.000{pn}>')
 
     def _take_line(self):
-        if b'\n' not in self.rx or len(self.planner) >= self.PLANNER:
+        if self.sleeping or b'\n' not in self.rx or len(self.planner) >= self.PLANNER:
             return
         raw, _, rest = bytes(self.rx).partition(b'\n')
         self.rx = bytearray(rest)
@@ -146,6 +149,10 @@ class FakeGrbl:
                 if ax in w:
                     tgt[i] = (self.mpos[i] + float(w[ax])) if rel else float(w[ax]) + self.wco[i]
             self.planner.append(['jog', tgt, float(w.get('F', 600))])
+        elif line == '$SLP':
+            self.sleeping = True
+            self.planner.clear()
+            self.state = 'Sleep'
         elif line.startswith('$X'):
             self.alarm = False
             self.state = 'Idle'
@@ -189,6 +196,9 @@ class FakeGrbl:
                 dt = real_dt * self.speedup
                 self.t_last = now
                 self._take_line()
+                if self.sleeping:
+                    self.state = 'Sleep'
+                    continue
                 if self.alarm:
                     self.state = 'Alarm'
                     continue