Improve request/response log field names

[dillonstreator]

Summary

• Rename Fastify defaults (reqId, responseTime, statusCode, remoteAddress, etc.) to clearer structured-log names
• Keep Fastifys req/res nesting with short relative fields (method, path, status_code, ...) and top-level request_id/duration_ms`

Test plan

• pnpm test passes
• Hit /hi and confirm logs include request_id, duration_ms, req.method, req.path, and res.status_code
• Confirm error responses still log with the updated res serializer fields