[good first issue] Add Cline (VS Code) setup guide

[GoDiao]

Goal

Add a copy-paste-ready setup guide for Cline (VS Code extension) in the README (or docs/agents/cline.md).

Required content

1. Settings path in VS Code
2. Values to fill in for OpenAI-compatible provider mode
3. Base URL: http://localhost:8787/v1
4. Model recommendations from Freeway

Acceptance criteria

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

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.