ci: bootstrap inert efficacy audit workflow

[Artexis10]

What changed

Adds the final .github/workflows/ci-efficacy-audit.yml filename to the default-branch line as an inert manual-dispatch bootstrap.

The workflow has one static one-minute job. It does not check out or execute repository code, accept inputs, use actions, install anything, access credentials, or publish audit evidence.

Why

GitHub only allows manual dispatch of a workflow by filename after that workflow exists on the default branch. This small bootstrap is the prerequisite for later dispatching an independently reviewed audit implementation from an exact branch revision.

Merging this PR does not run the mutation audit and does not change required CI.

Safety contract

• workflow_dispatch only
• permissions: {}
• no checkout, actions, token, secrets, writes, mutation, or installation
• no push, pull-request, target, schedule, or hosted-live authority

Verification

• exact-content and forbidden-property structural checks passed before and after commit
• git show --check passed
• independent config/security review: no findings, approved

Local full Go baseline was also attempted; it is not usable as a signal in this restricted Windows sandbox because pre-existing registry and profile tests receive host Access is denied errors. This workflow-only change does not touch Go code.