Implement core Lucid x402 search API

[minyanyi]

Summary

• adds a Bun/Hono server entrypoint with free /health and paid /v1/search, /v1/search/news, and /v1/search/deep endpoints
• adds Zod v4 request/response/error schemas with JSON Schema export
• wires search orchestration through Brave results, ranking, cache, freshness metadata, and GPT synthesis fallback
• adds Lucid Agents + x402 payment dependencies and a Lucid agent builder using paymentsFromEnv()
• documents required environment variables in .env.example and README

Tests

• bun run typecheck
• bun test (43 passing)

Fixes #1.

TaskMarket payout

USDC/EVM payout address: 0x2E4380d2e1668Ca9fA3Ef91fF776FDc140Cf3fE8