Add deterministic regression benchmark and update validation docs

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## 0.3.0 — reproducible evidence scaffold
 
-Verified locally with the checked-in `run_checks.ps1` gate (28 tests):
+Verified locally with the checked-in `run_checks.ps1` gate (29 tests):
 
 - V2 depth baseline with optional DA3 camera-aware adapter and early contract
   validation.
@@ -15,6 +15,8 @@ Verified locally with the checked-in `run_checks.ps1` gate (28 tests):
 - Image-space and depth-normal photometric lighting hypotheses.
 - Projection coverage and relative-depth reprojection diagnostics.
 - Explicit CPU export smoke test and Docker HTTP health check.
+- Deterministic CPU regression harness across three fixture resolutions, with
+  repeat signatures and machine-readable fusion metrics.
 - Pinned Torch/TorchVision baseline and commit-pinned optional DA3 research
   dependency.