Implement PostgreSQL production store path

Add the PostgreSQL backend, migration and stopped-write transfer tools, lease-aware deployment manifests, tenancy declarations, and shared conformance coverage. Persist grouping mutations in durable stores and separate process liveness from database readiness.

tests/test_app.py

@@ -11,3 +11,16 @@ def test_health_endpoint() -> None:
     body = response.json()
     assert body["status"] == "ok"
     assert body["service"] == "tenant-engine"
+    assert body["store_backend"] == "memory"
+
+
+def test_liveness_endpoint_does_not_depend_on_the_store() -> None:
+    class _UnavailableStore:
+        def ping(self) -> None:
+            raise AssertionError("liveness must not touch the store")
+
+    client = TestClient(create_app(store=_UnavailableStore()))
+    response = client.get("/live")
+
+    assert response.status_code == 200
+    assert response.json()["status"] == "ok"