feat: ship pixelbrowse as an opencode plugin

[tauanbinato]

Summary

Closes #117.

Adds plugin/opencode/ — an npm package (opencode-pixelbrowse) so opencode users can load pixelbrowse under "plugin" in opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "plugin": ["opencode-pixelbrowse"]
}

The plugin registers a screenshot custom tool (via @opencode-ai/plugin) that:

• runs pixelshot <target> --output /tmp/pixelbrowse --tile-height 1568 (plus --wait-network-idle for URLs) — the same visual-readability defaults the Claude Code skill mandates
• supports URLs, local HTML files, PDFs, and images, with optional output and viewportWidth args
• returns the sorted tile image paths so the agent reads them directly with its Read tool
• embeds the skill's key guidance in the tool description (when to use, tile ordering, Pillow crop-and-zoom for small text)
• returns a friendly install hint (uv tool install pixelrag / pipx / pip) when pixelshot is not on PATH

Also adds an opencode note in plugin/README.md and the main README's "Give Claude eyes" section.

Notes for maintainers

• Publishing: the package is not published yet — npm publish --access public from plugin/opencode/ (documented in its README). Happy to adjust the package name if you'd prefer a scoped one (e.g. @startrail/pixelbrowse).
• Validation done: node --check, npm pack --dry-run, and an import smoke test (PixelbrowsePlugin loads and registers the screenshot tool). Not yet exercised end-to-end inside a live opencode session.

Test plan

• Maintainer: npm publish --access public from plugin/opencode/
• With pixelshot on PATH, add "plugin": ["opencode-pixelbrowse"] to opencode.json and run e.g. opencode run "screenshot https://news.ycombinator.com and summarize the top stories"

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