webfetch skips HTML conversion for mixed-case media types

Description

webfetch skips HTML conversion when the server uses different casing in its media type.

For example, a response with:

Content-Type: Text/HTML; Charset=UTF-8

passes the textual-content check, but format: "markdown" and format: "text" return the raw HTML. The conversion path checks the original header with a case-sensitive includes("text/html").

HTTP media types are case-insensitive. Mixed-case text/html values should behave like lowercase text/html.

Plugins

Built-in webfetch only.

OpenCode version

V2 source at ba753b383f678896eb8df8f243faecc9f4e27c66.

Steps to reproduce

1. Return <h1>Hello</h1> with Content-Type: Text/HTML; Charset=UTF-8.
2. Call webfetch with format: "markdown".
3. Observe raw <h1>Hello</h1> instead of # Hello.

Operating System

macOS arm64.