bootstrap: planned object-storage reef, no rail

Declare reef-storage as substrate_kind object-storage. Hold non-secret
attribute paths for Scaleway S3. Do not host a compute rail.

INTENT.md

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+# INTENT
+
+## Why This Repo Exists
+
+`reef-storage` is the substrate boundary for **provider-delegated
+S3-compatible object storage**. The first instance is Scaleway, used for
+postgres backup and other large, slow-tolerant volumes.
+
+We consume the S3 capability. We do **not** host a rail and we do **not**
+operate how Scaleway provides or runs object storage. This reef names the
+boundary, holds the committed non-secret attributes, and is the place
+operators look for “where is our object store?”
+
+It is a different reef from `reef-railiance`. Backup is not bolted onto
+the home compute substrate.
+
+## What This Repo Must Protect
+
+- the split: procure/cost in `resource-control`, operate-by-reference here,
+  secrets in `railiance-platform`, consume in `rapp-*`
+- no rail invented to satisfy a compute-centric schema
+- no secret material in git
+- independent failure domain from Host Europe / `reef-railiance`
+
+## What This Repo Is Not
+
+- a Scaleway account manager or billing ledger
+- a Barman/CNPG operator (`rapp-postgres`)
+- a secret store
+- a generic S3 client library
+- an extension of `reef-railiance`