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.

SCOPE.md

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+# SCOPE
+
+## One-liner
+
+Provider-delegated S3-compatible storage reef: identity and non-secret
+attributes, not a rail, not a secret store.
+
+## In Scope
+
+- Reef declaration (`substrate_kind: object-storage`, no rail)
+- Committed non-secret object-store attributes (endpoint, region, bucket,
+  prefix, versioning/lifecycle flags, provider project ref)
+- Runbooks for “how we use the delegated store,” not how Scaleway runs it
+- Binding notes for consumers (`rapp-postgres` first)
+
+## Out of Scope
+
+- Purchase approval, forecasts, settlement (`resource-control`)
+- Access keys and OpenBao delivery (`railiance-platform`)
+- WAL archive, backup schedule, restore (`rapp-postgres`)
+- Hosting Kubernetes or any rail
+- Implementing S3
+
+## Getting Oriented
+
+- Declaration: `declarations/reef.yaml`
+- Attribute contract: `schemas/object-store-attributes.schema.json`
+- Attribute files: `substrate/object-stores/`
+- Join convention: `resource-control/docs/operational-reference-convention.md`