infra(data): exporter (Parquet/CSV → R2) + reconciler (folded-state drift)

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Railway crons: exporter (DuckDB → partitioned Parquet/CSV in a public R2 prefix + a /api/v1/datasets manifest) and reconciler (diff folded balances/stake/yield vs runtime truth, alert on drift). Deliverable: public dataset exports + a drift-detection harness gating trust in portfolio/yield numbers.

Part of #2108. See ADR 0013 (docs/adr/0013-hybrid-deployment-topology.md) + runbook (deploy/README.md).