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/config.py

@@ -26,6 +26,8 @@ DEFAULTS = {
     },
     'motion': {
         'ball_speed_mm_s': 25.0,   # drawing speed of the ball across the sand
+        'motors_off_when_done': True,   # switch the motors off when the designs are done or stopped
+                                        # (quiet, cool); the next design homes first
         'max_theta_deg_s': 60.0,   # arm spin limit (10 rpm)
         'max_rho_mm_s': 25.0,      # carriage limit
         'theta_accel_deg_s2': 120.0,