Improve paid MCP guide and vendor lead discovery output

[Qyra-One]

Summary

Bounty-oriented contribution for the MYA Pyrimid micro-bounties:

• Job 24 ($10 USDC): expands examples/mcp-paid-tool/README.md into a practical paid MCP tool guide with endpoint shape, HTTP 402/x402 examples, catalog metadata, curl + TypeScript snippets, and an agent reproduction checklist.
• Job 25 ($20 USDC): improves the vendor-lead-discovery seed product output from three generic rows into ranked/scored lead templates by segment, with discovery queries, outreach angles, disqualification flags, and next steps.

Changes

• Adds a reproducible paid MCP guide for preview → 402 → payment retry → receipt/result flow.
• Adds lib/vendor-lead-discovery.ts with structured lead scoring for mcp, agent-frameworks, and api-tools segments.
• Updates /api/v1/paid/vendor-lead-discovery to use the richer output and support a bounded limit query param.
• Updates the catalog output_schema/description for the richer lead-discovery payload.

Verification

• npm ci --ignore-scripts
• npx tsc --noEmit
• git diff --check
• Changed-line secret-pattern scan: no hits
• Live read-only check confirmed current public seed endpoint returns HTTP 402 with x402 accepts[] metadata; no wallet/payment/KYC action was attempted.

Safety notes

No wallet/private key, live x402 purchase, paid service, KYC, or payout setup was used for this PR. This is only a docs/code deliverable for maintainer review and bounty acceptance.