feat: add live vendor lead discovery

[mateoalifraco]

Summary

• make vendor-lead-discovery return live GitHub-based lead candidates by segment when available
• add scoring signals for MCP/x402/Base/API fit and adoption
• include fallback leads, discovery-source metadata, outreach template, and next actions in clean JSON

Bounty

MYA/Pyrimid job #25: improve vendor-lead-discovery output ($20 USDC)

Payout

Base USDC: 0x97620eB52A577cabc95911099E88e83115eB7C20

Verification

• npx tsc --noEmit
• npm run build
• git diff --check
• secret scan over diff: no secrets/tokens/keys