feat(templates): add OpenAPI-first CRUD app scaffold with mock data

- include CRUD OpenAPI spec
- add in-memory mock data store
- implement OpenAPI-bound route handlers
- provide runnable FastAPI bootstrap
- include end-to-end integration test

openapi_first/templates/crud_app/main.py

@@ -0,0 +1,8 @@
+from openapi_first.app import OpenAPIFirstApp
+import routes
+
+app = OpenAPIFirstApp(
+    openapi_path="openapi.yaml",
+    routes_module=routes,
+    title="CRUD Example Service",
+)