[good first issue] Add Continue.dev setup guide

[GoDiao]

Goal

Add a copy-paste-ready setup guide for Continue.dev in the README (or docs/agents/continue-dev.md).

Required content

1. Config file location (~/.continue/config.json or project-level)
2. JSON snippet:

   {
     "title": "Freeway",
     "provider": "openai",
     "model": "llama-3.3-70b",
     "apiBase": "http://localhost:8787/v1",
     "apiKey": "your FREEWAY_API_KEY"
   }

3. How to pick a model from Freeway's catalog
4. One verification step

Acceptance criteria

• A new user can follow the guide and have Continue.dev talking to Freeway in under 2 minutes
• The guide is linked from the main README