chore: add step-by-step OpenAPI conversion demo

Add tools/api-format-to-openapi/demo-steps.mjs and npm scripts demo/demo:pause; ignore demo-output and document usage.

tools/api-format-to-openapi/package.json

@@ -5,6 +5,8 @@
   "description": "Конвертация доменного api-format в OpenAPI 3.0 (детерминированно или через LLM)",
   "scripts": {
     "convert": "node convert.mjs --in examples/api-format.example.json --out ../../openapi.generated.json",
-    "convert:llm": "node convert.mjs --mode llm --in examples/api-format.example.json --out ../../openapi.llm.json"
+    "convert:llm": "node convert.mjs --mode llm --in examples/api-format.example.json --out ../../openapi.llm.json",
+    "demo": "node demo-steps.mjs",
+    "demo:pause": "node demo-steps.mjs --pause"
   }
 }