feat(worker): improve log

[gmurayama]

Note

Low Risk
Logging-only changes around existing DB update failures; no functional changes to job creation or processing logic.

Overview
Improves observability in createDirectBatchesJobWithOption by emitting structured zap error logs when updating total_tokens or total_batches in Marathon DB fails (including job_id and computed counters).

Also includes a small formatting cleanup in the /stats handler and comment spacing (no behavior change).

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