Record the decision to adopt Stryker.NET (pinned local tool, solution mode on
Acl.slnx) and to set the first repo-wide mutation baseline on the ACL: observed
95%, enforced break threshold 90%. Document the ratchet, local run, and report
location in the CI runbook; add the ADR to the docs nav.
Proposed in #51 (adr-proposal). Refs #47.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
