Finish RAILIANCE-WP-0021: family schemas, validator, and ADR-0007

Add rail and reef schemas, derive reef bound_rapps from rapp.bound_reefs,
and ship a standalone family-declaration validator with an inventory-fed
coverage check. Point the bootstrap contract at the schemas, record the
dimension and cardinality decisions in ADR-0007, correct the first-wave
candidates document, and release the shape to downstream repos.

tools/testdata/family-declarations/good/reef-example/declarations/reef.yaml

@@ -0,0 +1,15 @@
+kind: substrate-reef
+reef_id: reef-example
+repo: reef-example
+ownership_repo: railiance-infra
+substrate_kind: server-group
+lifecycle_state: active
+criticality: high
+primary_rail: rail-kubernetes
+hosted_rails:
+  - rail-kubernetes
+  - rail-knative
+bound_rapps:
+  - rapp-example
+current_members:
+  - Example01