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.

declarations/reef.yaml

@@ -0,0 +1,20 @@
+kind: substrate-reef
+reef_id: reef-storage
+repo: reef-storage
+ownership_repo: railiance-platform
+substrate_kind: object-storage
+lifecycle_state: planned
+criticality: high
+current_members: []
+source_documents:
+  - repo: railiance-master
+    path: docs/reef-substrate-model.md
+  - repo: railiance-master
+    path: workplans/RMASTER-WP-0022-establish-reef-storage.md
+  - repo: resource-control
+    path: docs/operational-reference-convention.md
+compatibility_notes:
+  - "S3-compatible capability is delegated to Scaleway. This reef does not host a rail and does not operate the object store internals."
+  - "Non-secret attributes (endpoint, bucket, region, prefix, lifecycle) live under substrate/object-stores/."
+  - "Credentials live in railiance-platform OpenBao. resource-control cites reef: and secret: references only."
+  - "This substrate is independent of reef-railiance. Backup is not provided on the home compute reef."