feat(ax-arm): add AX-series arm robot package

Add the lerobot_robot_ax_arm package with the AXArm robot,
its config, URDF joint mapping, an end-effector keyboard
teleop example, and packaging metadata.

lerobot_robot_ax_arm/README.md

@@ -0,0 +1,49 @@
+# lerobot_robot_ax_arm
+
+A third-party [LeRobot](https://github.com/huggingface/lerobot) robot: a 4-DoF arm driven by Dynamixel
+AX-series servos (e.g. AX-12A) over **Protocol 1.0**.
+
+| Motor ID | Joint           | Normalization |
+| -------- | --------------- | ------------- |
+| 1        | `shoulder_pan`  | [-100, 100]   |
+| 2        | `shoulder_lift` | [-100, 100]   |
+| 3        | `elbow_flex`    | [-100, 100]   |
+| 4        | `gripper`       | [0, 100]      |
+
+## Protocol 1.0 notes
+
+AX-series motors differ from the X-series (Protocol 2.0) used elsewhere in LeRobot:
+
+- **No Sync Read** — positions are read sequentially (`get_observation` / calibration). Sync Write is still
+  used for `Goal_Position`.
+- **No `Operating_Mode` / PID registers** — `configure()` only lowers the return delay time.
+- **No homing offset register** — calibration records the range of motion only (`homing_offset = 0`) and is
+  stored via the CW/CCW angle limits.
+
+## Install
+
+```bash
+pip install -e .
+```
+
+This is discovered automatically by LeRobot thanks to the `lerobot_robot_` package prefix.
+
+## Usage
+
+```bash
+lerobot-record \
+  --robot.type=ax_arm \
+  --robot.port=/dev/tty.usbserial-AL02L1E0 \
+  # ... other arguments
+```
+
+Or from Python:
+
+```python
+from lerobot_robot_ax_arm import AXArm, AXArmConfig
+
+robot = AXArm(AXArmConfig(port="/dev/tty.usbserial-AL02L1E0"))
+robot.connect()
+obs = robot.get_observation()
+robot.disconnect()
+```