Add determinism tests for verdict artifact generation and update SHA256 sums script

- Implemented comprehensive tests for verdict artifact generation to ensure deterministic outputs across various scenarios, including identical inputs, parallel execution, and change ordering.
- Created helper methods for generating sample verdict inputs and computing canonical hashes.
- Added tests to validate the stability of canonical hashes, proof spine ordering, and summary statistics.
- Introduced a new PowerShell script to update SHA256 sums for files, ensuring accurate hash generation and file integrity checks.

docs/migration/enable-reachability.md

@@ -1,25 +0,0 @@
-# Enable Reachability — Draft Skeleton (2025-12-05 UTC)
-
-Status: draft placeholder. Inputs pending: DOCS-SIG-26-007, notifications hooks (058_NOTY0101), rollout telemetry contract.
-
-## Purpose
-- Describe why reachability is being enabled and expected outcomes.
-
-## Rollout Phases
-- Phase 0: prerequisites (feature flags, config keys).
-- Phase 1: limited tenants / canaries.
-- Phase 2: org-wide rollout with monitoring gates.
-
-## Fallbacks
-- How to disable/revert; config toggles; cache/queue drains.
-
-## Monitoring & Alerts
-- Metrics to watch (ingest lag, signal volume, error ratios).
-- Alert thresholds and runbooks (link when available).
-
-## Controls & Policy
-- Imposed rule reminder; RBAC/tenant scope considerations.
-
-## Open TODOs
-- Fill concrete config keys and examples when DOCS-SIG-26-007 lands.
-- Add notification hook wiring details from 058_NOTY0101.