Replace the PiCameraSource NotImplementedError stub with a working picamera2 CSI
source (SourcePort read()->(ok,frame), RGB888->BGR to match the pose adapters;
picamera2 lazy-imported as a system package, injected fake in tests). daemon.main()
gains CAMERA_BACKEND (csi|uvc) selecting PiCameraSource or UvcSource.
Replace the NotImplementedError stub with a working HailoPoseAdapter for Pi5 +
Hailo-8. yolov8s_pose has no on-chip NMS, so the adapter does host-side DFL box
decode + keypoint decode + greedy NMS + letterbox un-map + COCO-17 assembly
(numpy decode ported from Hailo's MIT PoseEstPostProcessing, locked by a synthetic
9-tensor unit test; the HailoRT device wiring is gated + device-validated on bringup).
daemon.main() gains a POSE_BACKEND switch (hailo|movenet).
