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/sandtable/web.py

@@ -275,6 +275,13 @@ class Player:
             finally:
                 c.guard = None
                 c.abort = False
+                if self.cfg['motion'].get('motors_off_when_done', True) and self.p.connected:
+                    try:
+                        c.motors_off()              # done or stopped: let the motors rest
+                        self.p.homed = False        # the arm can drift now, so home before the next one
+                        log('motors off')
+                    except Exception as e:
+                        log(f'could not switch the motors off: {e!r}')
                 self.now = None
                 self.state = 'idle'