Renew your own claim on a queued alarm (renew-only heartbeat)

The active-review heartbeat. RENEW-ONLY by construction: it restarts the TTL if and only if the caller still holds a live claim on a queued alarm, and it never acquires a free, lapsed or foreign claim, whatever the configuration. Always answers renewed (true: claim is the renewed claim; false: claim is the live claim of whoever holds it now, or null when the alarm is free, lapsed, closed or not on the active queue). A 404 may mean this route is unavailable on an older or disabled task (CLAIM_CLEANUP_ENABLED off), or that the event ID is unknown or malformed. Treat every error as unknown, never as renewed, and never fall back to acquire. Read claim_cleanup_enabled on GET /auth/me first. Customer-side callers get null and never staff identity. Requires claim participation (review_label_alarms, or, for central staff, any of escalate_voice_down, escalate_dispatch, notify_property_owner: whoever the claim refusal can refuse) and tenant scope (out of scope is 403, unknown or malformed id is 404).