fix: prevent document ingestion finalization errors

[suguanYang]

Summary

• make S3 upload and confirm-upload handoff idempotent for the same job
• skip duplicate worker deliveries when the processing lock is held
• deduplicate sanitized document chunk paths before publication
• remove PostgreSQL-incompatible NUL characters at the persistence boundary while preserving the original result archive

Why

The staging Logfire alerts showed three correctness failures:

1. S3 upload and confirm-upload could enqueue two deliveries for one logical job; the losing delivery could eventually fail/refund the active job.
2. Parser output could contain duplicate non-null source_chunk_path values, violating uq_document_chunks_revision_path.
3. Parser text or metadata could contain NUL characters, causing PostgreSQL persistence to fail after parsing completed.

Verification

• API handoff contract tests: 3 passed
• Worker processing/publication contract tests: 4 passed
• Ruff: passed
• git diff --check: passed

Production was not changed by this PR.