Add Cursor marketplace plugin manifest

[fatwang2]

What changed

• add .cursor-plugin/plugin.json for the official Cursor Marketplace
• expose the existing Search1API skill and remote MCP server through the Cursor plugin package
• reuse the public integration docs, repository metadata, MIT license, and Search1API icon

Why

Cursor Marketplace submissions require a public repository with a valid .cursor-plugin/plugin.json. This manifest makes the existing Search1API skill + MCP packaging discoverable and reviewable by Cursor.

Impact

After this lands on the default branch, the repository can be submitted through Cursor's Marketplace publisher form. No runtime CLI behavior changes.

Validation

• Cursor official JSON Schema: .cursor-plugin/plugin.json valid
• referenced files: icon, .mcp.json, and skill all present
• integration docs URL: HTTP 200
• npm test: 4/4 passed
• git diff --check

Local Cursor installation testing was not available because Cursor is not installed on this machine.