Package Hunter's hosted Streamable HTTP MCP server
(https://mcp.hunter.io/mcp) using the official Cursor setup from
https://hunter.io/agents.md: X-API-Key with ${HUNTER_API_KEY}.
This is a fresh-from-main take on #317, which used OAuth-only config
and documented the API key as an opt-in alternative. Official Cursor
packaging is header auth, so plugin.json declares the HUNTER_API_KEY
template variable the same way other BYO-credential plugins do.
Co-authored-by: Sam Sokolin <SamSokolin@users.noreply.github.com>