[governance] Resolve unreachable DeviceRegistry.setDayOwner/3 on both platforms

[bhelm]

Confirmed reachability debt

The parity ledger Kotlin-template arity fix makes plain string arguments occupy their real call argument. That exposes the existing Android declaration DeviceRegistry.setDayOwner/3 as test-only: three exact test callsites and no production callsite. The Swift twin is likewise production-declared/test-only.

This is independently confirmed upstream in ryanbr#981, including an owner review that verifies the feature is unreachable on both platforms: the day-owner reader runs in production, but no shipping path can write a locked owner.

Exact fork ledger identity:

test-only-callsite|android/app/src/main/java/com/noop/data/DeviceRegistry.kt::setDayOwner/3#1

Acceptance

• Re-audit exact production reachability on both Swift and Kotlin; tests, declarations, DAO forwarding, twin-map suggestions, and parity exemptions do not count as a production caller.
• Make an explicit product disposition: either wire a real user/runtime path to set a locked day owner on both platforms, or remove the unreachable API and locked-owner branch on both platforms.
• Add focused tests for the chosen shipping behavior and preserve cross-platform parity.
• Remove the exact issue-bound ledger baseline finding once a real production caller exists or the declaration is removed.
• Do not satisfy this issue by adding a broad exemption or weakening callsite/arity detection.

Upstream provenance: ryanbr#981