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/rapp-example/declarations/rapp.yaml

@@ -0,0 +1,34 @@
+kind: managed-workload-package
+repo_family: rapp
+rapp_id: rapp-example
+repo: rapp-example
+ownership_repo: railiance-platform
+contract_version: 1.0.0
+readiness_state: declared
+workload_identity:
+  name: example
+  package_type: helm-managed-platform-service
+data_classification: internal
+criticality: medium
+primary_rail: rail-kubernetes
+supported_rails:
+  - rail-kubernetes
+bound_reefs:
+  - reef-example
+runtime_dependencies:
+  - kubernetes-api
+composition:
+  purpose: Example single-repo rapp used as a validator fixture.
+  member_repos:
+    - repo: rapp-example
+      role: package
+      deployables:
+        - example
+rollout_contract:
+  default_mode: helm-upgrade-install
+smoke_contract:
+  required:
+    - example-status-ok
+rollback_contract:
+  order:
+    - helm-rollback