Add Netlify and Render deployment skills

[vb-openai]

Summary

• add the curated netlify-deploy skill to the existing Netlify plugin and refresh its metadata/icons
• add a new render plugin with the curated render-deploy skill, root assets, and Render MCP config
• register render in .agents/plugins/marketplace.json

Source

• vendored from openai/skills origin/main at ecc1fb8

Validation

• git diff --cached --check
• python3 /Users/vb/Documents/plugins-internal/scripts/validate_plugin.py plugins/netlify
• python3 /Users/vb/Documents/plugins-internal/scripts/validate_plugin.py plugins/render

Notes

• installer smoke test not run because this openai/plugins checkout does not include the installer script