feat: add Leads tab and Hide Assessed filter in Browse
- db.py: get_enriched() accepts ai_only + lead_quality params
- main.py: /api/enriched exposes ai_only + lead_quality query params;
new /api/export/leads endpoint produces CSV with contacts + pitch
- index.html:
- New "Leads 🤖" tab shows all AI-assessed domains with contacts
(quality/country/limit filters, per-row 📋 copy email, 🔍 modal,
CSV export, pagination, auto-refreshes every 3s)
- Browse: "Hide assessed" checkbox filters out already-processed
domains so you can focus on fresh targets
- Poll cycle refreshes Leads tab when active
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>