Pause now holds the pipeline without tearing it down: CAPTURE_ONLY keeps the camera
streaming so a live sensor stays converged while the flow and HHD stages stop, and BOTH stops
the read as well. Resume rebases the tracker, because a held reference frame would otherwise
report the hold itself as deformation.
Verified with tests/test_pipeline_pause.py: 10 passed across three consecutive runs.
ykcheungab