chore: prepare permanent Render deployment

[Videirafo]

Closes #21

What this adds

• Render Free web-service Blueprint for the real FastAPI Playground;
• /health contract and CI-gated deploy configuration;
• one-click Deploy to Render guide;
• external launch kit for Show HN, DEV, Reddit and LinkedIn;
• dedicated Blueprint validation workflow.

Constraints preserved

• GitHub remains the source of truth;
• no new source repository;
• no secrets, database or LLM provider;
• no coupling to MarcaIA or unrelated hosting projects.

The canonical live URL will be added only after the Render service is created and internet-smoke-tested.