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/cli.py

@@ -353,6 +353,18 @@ def cmd_play(cfg, args):
 
 
 def _play(c, cfg, args, items):
+    try:
+        _play_list(c, cfg, args, items)
+    finally:
+        if cfg['motion'].get('motors_off_when_done', True):
+            try:
+                c.motors_off()                  # done, stopped or failed: let the motors rest
+                print('  motors off')
+            except Exception:
+                pass                            # e.g. the USB link has gone
+
+
+def _play_list(c, cfg, args, items):
     if not args.no_home:
         print('  homing rho ...', flush=True)
         c.home_rho(cfg)