[connectors] Web-search connector (Google Custom Search / SerpAPI) — enrichment #99

Child of #94, child of #84.

Enriching leads with socials/email (Instagram, Facebook, email) needs web search — not available today. Add a web-search connector so an enrich step (#94) can look a business up and extract links.

Do

• Connector wrapping Google Custom Search (free tier; key + CSE id from vault) and/or SerpAPI, exposing a web_search(query) → results[] tool.
• A companion extract step (or map step, #step-library) to pull instagram.com / facebook.com / mailto: from result pages.
• Rate-limited + audited; results are best-effort (note precision in output).

Acceptance

• An enrich step can take a business name+suburb and populate instagram / facebook / email columns.