fix: export ConvertedHtml interface

[emmclaughlin]

Summary

Exports the ConvertedHtml interface from src/utils/render.ts so consumers can reference the return shape of render() by name instead of redefining it locally.

Motivation

Resolves #153. A user requested this so they can type their own functions that accept/produce the result of render() without copying the interface into their own codebase.

Notes

• The shape is already effectively part of the public API via the render() return type, so this just gives it a named, importable handle.
• No behavior change; no breaking change.
• The interface only references types already public from mjml-core (MJMLJsonObject, MJMLParseError).

Testing

• yarn lint — passes
• yarn build-cjs — passes
• yarn test — 91/91 passing

[faire-samurai]

🤖 Agent sessions

• 🧑‍💻 feat: export `ConvertedHtml` interface (RUNNING)

_{Updated at 2026-06-01T13:04:03.103Z}

[emmclaughlin]

/merge