Implement status field, derived from adverised_start_time

[benrobey]

Step 3: Race Status (OPEN / CLOSED)

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Feature: Each race now includes a status based on advertised_start_time relative to "now".

• OPEN => start time is in the future
• CLOSED => start time is now or in the past

Status field is always present.

Example: Show first few races with status

curl -s -X POST localhost:8000/v1/list-races -d '{}' \
  | jq '.races[0:5] | map({id, status, start: .advertisedStartTime})'

Example: Only future (OPEN) races

curl -s -X POST localhost:8000/v1/list-races -d '{}' \
  | jq '.races | map(select(.status=="RACE_STATUS_OPEN"))'