nx_h264_bframe_probe.nx

nx_h264_bframe_probe.nx -- B-R0: parse the GOP STRUCTURE of an annexb H.264 stream with B-frames (knowledge/staging/media/bframe_test.264, made by x264 --no-cabac --bframes 1). Splits annexb NALs, parses SPS/PPS, and for every slice prints (decode-order idx, nal_type, slice_type I/P/B, frame_num, poc_lsb, nal_ref_idc) -- revealing decode order vs display (POC) order and which frames are B + their reference role. Foundation for the B-frame decode arc (ref-list construction, bi-prediction). Exit 0.