refactor: manual mode from absolute setpoint to velocity control, remove auto-enable at motor init

Manual mode now receives angular velocity (degrees/s) via 0xA6 frame instead of
absolute angle reference. The firmware integrates velocity * dt into gimbal angle ref.
Motors are no longer auto-enabled at DMMotorInit — they stay disabled until a mode
switch out of DEBUG. Extract ROBOT_CMD_DELAY macro to replace magic number.
Fix "volity" typo → "velocity" and update docs/protocol comments accordingly.

modules/motor/DMmotor/dmmotor.c

@@ -191,9 +191,6 @@ DMMotorInstance *DMMotorInit(DM_Motor_Init_Config_s *config)
     };
     //motor->motor_daemon = DaemonRegister(&conf);
 
-    /* enable motor */
-    DMMotorSetMode(DM_CMD_ENABLE_MODE, motor);
-
     dm_motor_instance[idx++] = motor;
     return motor;
 }