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.

application/robot_def.h

@@ -5,6 +5,9 @@
 #include "ins_task.h"
 #include "stdint.h"
 
+// 机器人核心任务的延时时间(ms)
+#define ROBOT_CMD_DELAY 2
+
 /* 开发板类型定义 */
 #define ONE_BOARD // 单板控制整车