feat(web-platform): release V0.4 balance control

wasm/web_platform/fixtures/python_controller/balance.py

@@ -0,0 +1,22 @@
+"""可信本地脚本示例：用 PD 控制让倒立摆保持竖直。"""
+
+NAME = "倒立摆 PD 平衡控制"
+CONTROL_HZ = 100
+
+
+def init(api):
+    return {
+        "joint": api.joint("balance_hinge"),
+        "actuator": api.actuator("balance_motor"),
+    }
+
+
+def step(ctx, state):
+    angle = ctx.qpos(state["joint"])
+    angular_velocity = ctx.qvel(state["joint"])
+    torque = -80.0 * angle - 12.0 * angular_velocity
+    ctx.set_control(state["actuator"], torque)
+
+
+def reset(state):
+    pass