Add lint rule rejecting directional SubTree ports

[L4co77]

Problem

SubTree ports are always bidirectional, but nothing stops an objective from declaring its SubTree interface with <input_port>/<output_port>. That mis-authored direction is invisible in the editor (the REST converter normalizes on read) yet leaks through the legacy XML endpoint, and it silently reappears in new objectives.

Approach

In validate_objective, fail when a SubTree definition declares any <input_port>/<output_port> child, naming the offending ports so the author knows what to change. Uses findall on the SubTree element directly, so only the interface declaration is checked — not behavior ports elsewhere.

Sequencing

Must merge after the example_ws migration (PickNikRobotics/moveit_pro#19906 → moveit_pro_example_ws#728). Enabling it earlier red-CIs the 41 existing official objectives.

Verification

Ran the rule against moveit_pro_example_ws v9.4:

• Pre-migration content: flags exactly the 41 objectives.
• Post-migration content: flags 0.

Refs PickNikRobotics/moveit_pro#19906

[Copilot]

Pull request overview

Adds a new validation rule to prevent mis-authored SubTree port directions in MoveIt Pro objective XMLs, ensuring SubTree interfaces are declared as bidirectional (<inout_port>) rather than directional (<input_port>/<output_port>), which can silently reappear via legacy XML flows.

Changes:

• Reject objectives whose TreeNodesModel/SubTree interface declares any <input_port> or <output_port> children.
• Improve failure output by listing the offending port names in the validation error.

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