feat(cli): add bundled health app scaffold and init command

- ship OpenAPI-first health check template as package data
- add CLI to copy scaffold into new project directories
- include OpenAPI spec, routes, and bootstrap example
- enable fast startup for OpenAPI-first services

openapi_first/templates/health_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="Health Check Service",
+)