Read velocity command range from ONNX metadata with config override

[kingb]

Summary

Ros2VelocityInput._callback() currently hardcodes the velocity clamp range to [-1, 1]:

self.policy.lin_vel_command[0, 0] = max(-1.0, min(1.0, msg.twist.linear.x))

The training range may differ per model. This should follow the same resolution pattern as KP/KD:

1. ONNX metadata — read vel_range (or similar) from model metadata
2. Config/CLI override — --task.velocity-range to explicitly set the range
3. Default — fall back to [-1, 1] if neither source provides a value

Context

Introduced in PR #89 (input provider model). The clamp values are correct for current models but should be configurable for future ones.

Acceptance criteria

• Velocity clamp range read from ONNX metadata when available
• Config/CLI override takes precedence over ONNX metadata
• Default to [-1, 1] when neither is provided
• Applied in Ros2VelocityInput._callback() (and any future velocity providers that need clamping)