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/inventory.json

@@ -0,0 +1,8 @@
+{
+  "source": "fixture",
+  "captured_at": "2026-08-13T00:00:00Z",
+  "reef": "reef-example",
+  "deployables": [
+    {"name": "example", "namespace": "example", "kind": "helm-release"}
+  ]
+}