Add robot-specific operational command limits

[s2015-turtle]

Summary

• add optional ROS joint-coordinate limits for position, velocity, and effort commands
• clamp commands before coordinate conversion and CAN encoding
• reject non-finite, reversed, or out-of-wire-range configurations
• expose the limits from every motor profile and document them in English and Japanese
• add parser, clamping, and Xacro coverage

Validation

• git diff --check
• XML validation for changed Xacro files
• expanded both the default profile fixture and explicit command-limit fixture with Xacro
• local build intentionally not run on this PC; the ROS distribution matrix will run in GitHub Actions

Closes #7