Backfill orchestrator should log BackfillResult outcomes

[kbighorse]

Context

Identified during review of #558 (558-radionuclides-backfill branch).

Problem

backfill.py calls fn(batch_size) but discards the BackfillResult return value. Operators see "Starting backfill" / "Completed backfill" with no detail on how many rows were inserted, updated, skipped as orphans, or errored.

Fix

Capture the return value and log the summary fields (inserted, updated, skipped_orphans, len(errors)). Log individual errors at WARNING level.

Files

• transfers/backfill/backfill.py (lines 48–50)

[github-actions]

Linked Jira ticket created: BDMS-614

[kbighorse]

Fixed in working tree — orchestrator now captures and logs BackfillResult summary.

[kbighorse]

Reopened to track completion on base branch. This should stay open until PR #569 is merged (the fix currently lives in that PR diff).