fix(6): fix argparse default for foreground mode

Changed default from 'foreground' (invalid choice) to None
Now correctly handles no arguments to start in foreground mode

Tested and verified:
  ✓ python3 start_servers.py        (foreground - all 3 services running)
  ✓ python3 start_servers.py start   (background)
  ✓ python3 start_servers.py status  (shows all services)
  ✓ python3 start_servers.py stop    (graceful shutdown)
  ✓ HTTP endpoints responding on 8916/8917
  ✓ HTTPS endpoints responding on 8918/8919 (Caddy)
  ✓ All three services (backend, frontend, caddy) working together

start_servers.py

@@ -495,7 +495,7 @@ Features:
         'command',
         nargs='?',
         choices=['start', 'stop', 'restart', 'status'],
-        default='foreground',
+        default=None,
         help='Command to execute (default: foreground mode)'
     )
 
@@ -512,6 +512,8 @@ Features:
         manager.run_background()
     elif args.command == 'status':
         manager.show_status()
+    elif args.command is None:
+        manager.run_foreground()
     else:
         manager.run_foreground()