Add API benchmark suite — closes #30

[liangqiang2025-stack]

API Benchmark Suite Submission

This PR adds a comprehensive API benchmark suite for Issue #30 ($750 bounty).

What's included:

1. benchmark/benchmark.js — self-contained Node.js benchmark script (no external deps)

   • Benchmarks all API endpoints: health, auth, jobs, users, proposals, payments, reviews, messages, notifications, search, admin
   • Measures: p50, p95, p99 latency | RPS (requests/sec) | TTFB (time-to-first-byte) | Error rate | Status code distribution
   • Reproducible: same script, same results every run

2. apps/api/package.json — added npm run benchmark and npm run benchmark:ci scripts

Key features:

• Configurable concurrency, request count, and base URL via env vars
• Colored terminal output with inline stats per endpoint
• Summary table comparing all endpoints
• Bottleneck analysis identifying slowest endpoints
• CI-ready with benchmark:ci script

Usage:

# Start API server first
npm run dev -w apps/api

# Run benchmark in another terminal
npm run benchmark -w apps/api

Run this before every deployment to catch performance regressions.