Test the native validator in CI, built against BehaviorTree.CPP

[kineticsystem]

Summary

• A second CI job, native validator, in a ros:jazzy-ros-base container: it builds the validator against the ROS package of BehaviorTree.CPP, the library and the version (4.10.0) the commander loads trees with, runs every test with the real validator, and validates the examples.
• tests/native-real.test.ts: the validator itself — a valid tree, a modelled node, an unknown node, a missing SubTree, an XML syntax error, and the built-in nodes it reports. Runs only where BTCPP_VALIDATOR_REAL names the built program; skipped elsewhere, e.g. in the existing job.
• validator/CMakeLists.txt links to whichever target the library exports: BT::behaviortree_cpp from a build from source (the Docker image), behaviortree_cpp::behaviortree_cpp from the ROS package.
• The CI badge in the README; the tests and the jobs in docs/ARCHITECTURE.md.

Until now every test ran against a fake validator, and the comment in ci.yml said the real one could not be built there.

Test plan

• The new job run with act on a clean clone: validator built, 137 tests pass (6 with the real validator), examples valid.
• Without the real validator: 131 pass, 6 skipped; type check passes.
• The validator still builds in the editor's Docker image, against BehaviorTree.CPP built from source.
• The run on GitHub.

🤖 Generated with Claude Code