Complete REUSE-WP-0005: registry federation and relation graphs

Add federation manifest and schema, federation compose and graph CLI commands,
relation cycle/reference checks, federated index and Mermaid graph artifacts,
RegistryFederation guide, and CI validation updates.

tools/README.md

@@ -61,6 +61,26 @@ reuse-surface catalog
 
 Writes `docs/CapabilityCatalog.md` and `docs/catalog/index.html`.
 
+### federation compose
+
+Compose a federated index from `registry/federation/sources.yaml`.
+
+```bash
+reuse-surface federation compose
+```
+
+Writes `registry/indexes/federated.yaml` with `source_repo` attribution.
+
+### graph
+
+Generate a Mermaid relation graph from capability entry relations.
+
+```bash
+reuse-surface graph
+reuse-surface graph --check
+reuse-surface graph --stdout
+```
+
 ## Export format
 
 The export bundle includes:
@@ -80,6 +100,8 @@ Stable IDs and maturity fields are preserved for agent consumption (UC-RS-019).
 | Export for agents | `reuse-surface export --format json` |
 | Detect overlap | `reuse-surface overlaps` |
 | Publish catalog | `reuse-surface catalog` |
+| Compose federation | `reuse-surface federation compose` |
+| Relation graph | `reuse-surface graph` |
 
 ## Related use cases