docs(register): make the status column describe the code

Eleven rows corrected, in both directions.

Overstated: AR-011 (the derived dedup window reached scenes.json only),
AR-017 (route was a literal), AR-019 (the local plurality tally was
still deciding), AR-024 (its "static check" enforcement did not exist),
DP-001 (scene_preview had forked and stopped compiling), VR-002 (the
Python replay bindings have not compiled since the tracker redesign, and
the fixtures it calls committed are gitignored registry artifacts).

Understated: VR-010 was marked Planned while five VR-010 tags sat in the
code implementing it.

Rescoped: VR-007 now names the four AR-025 constants it was already
being deferred to for, and which no sweep could reach until this pass.

The Withdrawn note gets the longest correction, because it asserted a
removal that had not happened and nothing could have caught that: the
gate reads tags, and a withdrawn requirement has no tag to be orphaned.
The general form is now written down there -- a status column is a
claim, and the only claims this project checks automatically are the
ones a test or a static check makes. Four of the rows above are the same
pattern: recorded as done, and done in one place out of two.

New: VR-016, a cadence study for cut_threshold. It is the one always-on
signal with no recorded provenance, and its input rate depends on an
unrelated flag -- with --scene-detect off, camera_pos compares frames a
full second apart at the default sample_fps, and with it on, native-rate
frames. Same constant, two meanings, and is_cut drives track_alpha to 0
and clears every expansion buffer.

Also stops check_raw_cosine.py inflating its own metric: the extractor
scans scripts/, so the tool's prose describing the exception tag was
counted as four recorded exceptions. The count now reads 1, which is the
number of real ones.

TRACES: AR-011, AR-017, AR-019, AR-024, AR-025 | DP-001, DP-007 | IR-004 | VR-002, VR-007, VR-010, VR-016

src/scene_preview.cpp

@@ -144,7 +144,7 @@ int main(int argc, char** argv) {
     FaceDetectorFunc    detector_fn{cfg};
     FaceAlignerFunc     aligner_fn;
     EmbedderFunc        embedder_fn{cfg};
-    /// TRACES: DP-001, AR-007, AR-012, AR-024 | PR-004, SR-002
+    /// TRACES: AR-007, AR-012, AR-024 | DP-001 | SR-002 | PR-004
     // Construction order matters and is the same as main.cpp's, deliberately:
     // the matcher fits (or loads) the calibration, the registry needs a
     // discounter built from it, and the tracker needs both. DP-001 says modes