Fix operator claimed lane visibility

[yvette-carlisle]

Summary

• keep claimed queue candidates visible when no local running lane matches them
• hide queue echoes for any matching active lane, even when WebSocket activity arrives before the next full snapshot
• add dashboard contract coverage for the claimed-without-local-lane case

Validation

• cargo nextest run -p decodex operator_dashboard_does_not_hide_claimed_queue_without_local_lane
• cargo nextest run -p decodex operator_dashboard_flow_counts_distinguish_intake_attention
• cargo nextest run -p decodex live_operator_status_snapshot_excludes_claimed_candidates_from_waiting_intake_count
• cargo make checks