diag(proof): make hash precision configurable + CI cross-microarch sweep

verify.py's HASH_QUANTIZATION_DECIMALS is now overridable via
PROOF_HASH_DECIMALS. Finding: the determinism divergence is NOT
Windows-vs-Linux — Windows and a second Linux box (ruvultra, same
numpy/scipy) produce identical hashes at every precision, including
ca58956c at 6 decimals. Only the GitHub Azure CI runner diverges
(667eb054), i.e. a CPU-microarchitecture pocketfft/BLAS reordering
(the #560 Skylake-vs-Cascade-Lake class).

Temporary diagnostic sweep step prints the CI runner's hash at decimals
6..2 so we can pick the coarsest precision that collapses the
microarch divergence to the common hash. Both the sweep step and the
PROOF_HASH_DECIMALS plumbing are removed/finalized in the follow-up.

Co-Authored-By: claude-flow <ruv@ruv.net>

.github/workflows/verify-pipeline.yml

@@ -58,6 +58,20 @@ jobs:
           print('Reference signal metadata validated.')
           "
 
+      - name: Quantization sweep (diagnostic — cross-microarch precision)
+        working-directory: archive/v1
+        env:
+          OMP_NUM_THREADS: "1"
+          OPENBLAS_NUM_THREADS: "1"
+          MKL_NUM_THREADS: "1"
+          VECLIB_MAXIMUM_THREADS: "1"
+          NUMEXPR_NUM_THREADS: "1"
+        run: |
+          for d in 6 5 4 3 2; do
+            h=$(PROOF_HASH_DECIMALS=$d python data/proof/verify.py --generate-hash 2>/dev/null | grep -i 'Computed:' | sed 's/.*Computed:[[:space:]]*//')
+            echo "SWEEP d=$d $h"
+          done
+
       - name: Run pipeline verification
         working-directory: archive/v1
         env: