POST /api/leads
Content-Type: application/json

{
  "name":            "Jane Smith",        // required
  "email":           "jane@acme.com",     // required
  "source":          "google",            // required
  "company":         "Acme Corp",
  "vertical":        "saas",
  "intent_signals":  ["demo-request", "pricing-viewed"]
}

// Response 201
{
  "lead": { "id": 42, "score": 82, "status": "qualified", ... },
  "score": 82,
  "status": "qualified",
  "breakdown": {
    "source_quality": 18,
    "behavioral": 22,
    "data_completeness": 25,
    "vertical_fit": 25
  }
}