Add Hunter third-party MCP plugin (API key header auth)

[SamSokolin]

Summary

Adds the Hunter marketplace plugin under third_party/hunter/, matching Hunter’s official Cursor setup (agents.md) and this repo’s BYO-credential template-variable pattern.

Hosted MCP: https://mcp.hunter.io/mcp (Streamable HTTP). Auth is an X-API-Key header with ${HUNTER_API_KEY} — not OAuth for this packaging.

"hunter": {
  "url": "https://mcp.hunter.io/mcp",
  "headers": { "X-API-Key": "${HUNTER_API_KEY}" }
}

plugin.json declares the HUNTER_API_KEY template variable the same way other API-key plugins do (e.g. Similarweb, GitHub, Brevo). Users create a key at https://hunter.io/api-keys (Free plan works). No secrets are committed.

Relation to #317

#317 (“Add Hunter third-party MCP plugin”) is still open and packages the same third_party/hunter path with OAuth-only mcp.json (URL, no header / no template var), documenting X-API-Key as an opt-in alternative.

This PR is a fresh branch from current main, not a second Hunter plugin path. It reuses #317’s logo/LICENSE and capability docs, then corrects auth to the official Cursor header model. Prefer this over merging #317 as-is.

Files changed

• third_party/hunter/mcp.json — HTTP server + X-API-Key: ${HUNTER_API_KEY}
• third_party/hunter/.cursor-plugin/plugin.json — manifest + HUNTER_API_KEY variable
• third_party/hunter/README.md — install/auth docs pointing at agents.md and api-keys
• third_party/hunter/CHANGELOG.md
• third_party/hunter/LICENSE
• third_party/hunter/assets/logo.png — Hunter fox mark from the hunter-io GitHub org
• .cursor-plugin/marketplace.json — register hunter
• README.md — catalog row

Test plan

• node scripts/validate-plugins.mjs (after npm install --no-save ajv ajv-formats)
• Install from Cursor Settings → Plugins or /add-plugin hunter
• Set HUNTER_API_KEY from https://hunter.io/api-keys (do not use test-api-key)
• Smoke test a free Discover query, then a Domain Search