Add S3 archive write-path foundation

[pthmas]

Summary

This PR adds the S3 archive write-path foundation for Atlas.

When archive is enabled, the indexer now writes a canonical per-block archive entry into PostgreSQL inside the same transaction as the normal indexed data, and a background uploader drains those entries to an S3-compatible object store as zstd-compressed JSON bundles.

This also adds archive state tracking, contiguous-head manifest generation, MinIO support for local debugging, and automated backend coverage for the archive flow.

Scope

Included in this PR:

• clap/config support for archive runtime settings
• archive_blocks and archive_state migrations
• canonical block + receipts archive bundle generation
• async S3 uploader with durable retry via PostgreSQL
• contiguous archive manifest at {prefix}/v1/manifest.json
• MinIO support in local docker-compose
• automated unit + integration tests for archive success, retry, and manifest behavior

Explicitly not included in this PR:

• atlas-server archive dump
• atlas-server archive restore
• any S3 read path
• any cache changes
• any API or frontend changes
• DA or metadata archival
• historical backfill of already-indexed blocks

This is intentionally part 1 only. A follow-up PR will add the operator-facing archive dump/restore commands on top of this foundation.

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