Why:
- Implements plan 001 Phase 3's upload orchestration.
Changes:
- ObjectStorage port and MinIO adapter, thread-offloaded per ADR-0017.
- Tenant-scoped repositories for api_keys, source_files, ingestion_jobs.
- upload_source_file implementing the two-transaction shape with
(tenant_id, domain, content_sha256) idempotency.
Impact:
- This phase stores bytes only -- chunks_indexed is always 0 until
Phase 4/5 add parsing/embedding.
