feat: DEFERRED records audit trail (ARCH-003)

[Muizzkolapo]

Summary

• Writes a DISPOSITION_DEFERRED disposition to the storage backend when a record is queued for batch processing, closing the observability gap where DEFERRED was the only status without a durable trail
• Clears DEFERRED dispositions when batch results land, ensuring records don't accumulate in a stale intermediate state
• Warns on orphaned DEFERRED records (queued but never returned) after batch completion

Changes (7 files)

File	What
storage/backend.py	Add DISPOSITION_DEFERRED constant + Disposition.DEFERRED enum member
processing/result_collector.py	Write DEFERRED disposition via _safe_set_disposition(), add deferred to CollectionStats, fire ResultCollectedEvent
logging/events/data_pipeline_events.py	Add total_deferred: int = 0 to ResultCollectionCompleteEvent (defaulted for backward compat)
llm/batch/services/processing_recovery.py	Clear DEFERRED disposition for every record when batch results arrive
workflow/managers/batch.py	Add _warn_orphaned_deferred() — diagnostic warning after batch processing
tests/unit/core/test_result_collector.py	5 new tests: disposition write, no-guid skip, stats counting, mixed statuses
tests/unit/wave3/test_enrichment_complete_event.py	Updated deferred test to verify disposition write instead of just status existence

Design decisions

• source_guid as record_id — matches every other disposition in the codebase; enables correlation when batch results come back (also keyed by source_guid)
• clear_disposition() before writing final status — avoids UNIQUE constraint issues and ensures clean state regardless of final outcome (success records get no disposition, only the DEFERRED is cleared)
• Orphan detection is diagnostic only — warning log, never raises. Telemetry must not crash the pipeline.

Test plan

• ruff check . — all clean
• pytest — 4305 passed, 2 skipped, 0 failures
• New tests verify: DEFERRED disposition write, stats counting, no-guid safety, mixed-status correctness

Closes #84

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