[BUG] Add User-Agent headers for Cloudflare providers

[mchenco]

Description

Cloudflare providers ( and ) currently send requests without an identifying User-Agent. We want to include an OpenCode User-Agent so Workers AI / AI Gateway can attribute traffic.

Plugins

None

OpenCode version

dev

Steps to reproduce

1. Connect to or via
2. Send a request
3. Observe that no custom User-Agent is sent (only defaults)

Screenshot and/or share link

No response

Operating System

All

Terminal

All