Backfill orchestrator should log outcomes and preserve tracebacks

[kbighorse]

Summary

• Capture and log BackfillResult summary (inserted/updated/skipped_orphans/errors) instead of discarding the return value
• Log individual errors at WARNING level for operator visibility
• Preserve full traceback on critical failure via exc_info=True instead of f-string

Refs

Closes #563, closes #564
Part of #558

Blocks

• Chemistry backfill should handle missing Observation during note creation #565 — chemistry backfill note-creation lookup hardening
• Chemistry backfill test cleanup should handle errors gracefully #566 — chemistry backfill test cleanup error handling
• AnalysisMethod test cleanup should be scoped to test-created IDs #567 — scoped AnalysisMethod test cleanup
• Backfill step definitions should populate or remove unused parameter_ids tracker #568 — unused parameter_ids tracker cleanup

These issues depend on code introduced by #558 and will be addressed on that feature branch.

Test plan

• No functional behavior change — steps tuple is currently empty on staging
• Verify logging output when backfill steps are wired up in BDMS-611: Implement Radionuclides backfill job and BDD step definitions #558

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Updates the backfill orchestrator’s logging so operators can see per-step outcomes and get full tracebacks on orchestration failures.

Changes:

• Capture each backfill step’s return value and log inserted/updated/skipped_orphans/error counts.
• Log individual step errors at WARNING level for visibility.
• Preserve traceback on critical failures by using exc_info=True in the __main__ exception handler.