feat(replay): the whole replay chain is C++, including the sink

The sae_kpn module has not compiled since the AR-007/AR-008 tracker redesign,
and was switched off at the build rather than patched because the fix is a
restructuring. Two failures, one cause.

It did not compile: `add_face_tracker` built FaceTrackerFunc from a Config
alone, and the tracker has required a TrackRegistry and a calibration since
association moved into probability space.

And presence was rebuilt in Python. `replay.py::build_minimal` merged
per-frame detections into windows by annealing gaps, which is what the
pipeline did before AR-012. The sink builds a window from a TrackRegistry
claim instead — the extent of a track an actor owned, starting when they
appeared rather than when recognition first succeeded. Those answer different
questions, so every sweep was tuning against a contract the shipped code had
stopped honouring.

Both follow from the seam being a factory per node. The chain has a
construction order — the matcher fits the calibration, the registry needs a
discounter built from it, the tracker needs both, and the sink needs the
registry's claims — and independent factories cannot express it, so the
tracker kept being built against a signature that no longer existed. One
`add_pipeline` mirrors main.cpp exactly and is now the only way to build the
chain, so the ordering cannot be got wrong again from Python. DP-001 is the
requirement behind it: a replay harness is a front-end, and its job is to
supply frames and read the result, not to re-derive presence.

Lifetimes needed a home. ResultSinkFunc holds `const Config&` and
`std::atomic<bool>&`, which under main() are locals in a frame outliving the
pipeline; there is no such frame when the network is built and torn down from
Python. ReplaySession owns both for the network's lifetime, keyed by network
and released explicitly — a sweep builds one network per replay and the sink
retains every annotation, so holding them forever would grow with films x
configs. Getting this wrong presented as an empty output_path: the sink
announced `[result_sink] writing ` and wrote nothing.

test_sae_kpn.py is ported rather than left behind. It called all three removed
factories and asserted on SceneAnnotations read back per frame; neither half
survives, so it now waits on pipeline_done and asserts on the file the sink
writes. Verified against gallery_lvface.h5: three frames through the real
chain, timestamps 0/1/2, truth file written. EOF is a control token the sink
flushes on and does not record, so three inputs give three frames, never four.

SAE_BUILD_KPN_BINDINGS goes back to ON.

TRACES: VR-011, VR-002 | DP-001 | PR-002

scripts/docs/run_holdout_all_models.py

@@ -79,10 +79,9 @@ def main():
                 "--dump", str(dump), "--gallery", str(gallery),
                 "--out", str(pred_path),
                 "--prob-threshold", str(cfg["prob_threshold"]),
-                # anneal_sec is replay-local now (it configures replay.py's
-                # own windowing, not the pipeline). extinction_sec is gone
-                # entirely with SceneTrackerFunc -- see AR-012/AR-013.
-                "--anneal-sec", str(cfg.get("anneal_sec", 10.0)),
+                # anneal_sec and extinction_sec are both gone: presence is
+                # the registry's, built from track extents (AR-012/AR-013), and
+                # replay.py no longer windows anything itself (VR-011).
                 "--expand-gallery",
             ]
             print(f"RUN {model}/{film['slug']}...", file=sys.stderr)