Read who is working a queued alarm (no claim is taken)

Read-only twin of POST /events/{id}/claim, for a console opening an alarm's deep link before its queue snapshot has loaded: it never takes, renews or clears a claim and sends no nudge. Same body as the POST: the live claim (operator_id, operator_name, claimed_at, expires_at, expires_in_seconds) whoever holds it, or claim: null when nobody does (free, or the alarm has left the active queue). Customer-side callers always 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). Also 404 while CLAIM_CLEANUP_ENABLED is off; consoles read claim_cleanup_enabled on GET /auth/me first, and treat any error here as unknown, never as free. activity (claim-lock R2) is the escalation activity on this alarm (a valid intent and/or live calls), present even when claim is null because activity outlives the claim; the activity key is omitted while CLAIM_ESCALATION_ENABLED is off.