Two new packages:
- saltybot_person_reid_msgs: PersonAppearance + PersonAppearanceArray msgs
- saltybot_person_reid: MobileNetV2 torso-crop embedder (128-dim L2-norm)
with 128-bin HSV histogram fallback, cosine-similarity gallery with EMA
identity updates and configurable age-based pruning, ROS2 node publishing
PersonAppearanceArray on /saltybot/person_reid at 5 Hz.
Pure-Python helpers (_embedding_model, _reid_gallery) importable without
rclpy — 18/18 unit tests pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
