tooling: complete WS2 settings audit (merge-options + labels + mirror-vars) + farm deadlock-confirm

[hyperpolymath]

Goal

Finish the read-only estate settings audit gaps and confirm the deadlock signal.

Do

• Per-repo pass for merge-button options (not in the list endpoint) + labels + *_MIRROR_ENABLED vars coverage.
• Run the farm ci-deadlock-audit (union main-HEAD + latest-PR) to convert the WS2 'upper-bound' 229-repo required-check figure into confirmed per-repo deadlocks.
• Feed standards#408 (settings standard). Read-only.

Context

WS2 report: dev-notes/estate-settings-audit-2026-06-22/.