Add Vercel skills plugin wrapper

[ashwinm-oai]

Summary

• add the Vercel skills port under plugins/vercel
• keep the plugin app-backed via .app.json
• make the manifest minimally Codex-friendly by wiring in skills, author name, keywords, and Codex interface metadata
• intentionally exclude ZIP packaging artifacts because the runtime skills do not depend on them

Notes

• kept homepage on vercel.com and avoided broader description rewrites
• did not add .mcp.json because vercel-labs/agent-skills does not publish an MCP server config

Validation

• validated plugins/vercel/.codex-plugin/plugin.json with jq

[cching-openai]

closing due to copy of other vercel plugin