P9 complete: compiled kernels validated (byte-identical, 78-80 GSA samples/min/core), scaling report

Graviton3 c7g.8xlarge, 360 GSE165845 arrays: 360/360 GTCs identical between the Rust
kernels and the pure-Python paths; 1 worker 78-80 samples/min (pure Python 29.6).
Scaling 1->8 workers efficiency 0.87-0.90; above that the 125 MB/s gp3 disk caps the
run (~620 samples/min) and, on a RAM disk, a fixed per-worker start-up cost limits a
360-sample batch to efficiency 0.48 at 32 workers (K-025). Worker state is pickled once.
docs/validation/P9.md, result JSONs, guide/README/CHANGELOG updates.

docs/validation/P9_identity_360.json

@@ -0,0 +1 @@
+{"gtcs": 360, "differ": 0, "sample_summary": "identical"}