[feat] Ship pixelbrowse as an opencode plugin

[esauflores]

Currently Claude Code only.
Can you publish it as an npm package so opencode users can add it under "plugin" in opencode.json?

[andylizf]

Good idea — pixelbrowse is a thin wrapper (a skill definition + pixelshot), so an npm-packaged opencode plugin is mostly packaging work. We'd take a PR for it; the pieces live in plugin/ and .claude-plugin/marketplace.json.