Status poll for a fire-now job created via the async POST path.

Returns the parsed kv blob — fields::

{
    "job_id": "<uuid>",
    "status": "queued" | "running" | "done" | "failed",
    "started_at": "<ISO-8601 UTC>",
    "finished_at": "<ISO-8601 UTC>" | null,
    "candidates_to_attempt": int,
    "candidates_attempted": int,
    "candidates_sent": int,
    "errors": [str, ...],
    "result": {... run_daily_cold_fire blob ...} | null,
    "params": {dry_run, quota, skip_idempotency},
}

404 when the job_id has no kv row (typo or already evicted — this module never evicts but a future GC sweep might).