feat: add API benchmark suite with autocannon

[capa8795-design]

Summary

Add a complete API benchmark suite using autocannon. Covers all 21 API endpoints with latency (p50/p95/p99), RPS, and error rate metrics. Includes a CI smoke benchmark that gates on configurable thresholds.

Changes

New files

• benchmarks/ — autocannon benchmark suite (benchmark.js, thresholds.json, README, .env.benchmark)
• .github/workflows/benchmark.yml — CI smoke benchmark on PR

Modified files

• package.json — added pm run benchmark\ script + autocannon devDependency
• apps/api/src/middleware/rateLimit.js — auto-disabled when BENCHMARK=1
• .gitignore — allow tracking .env.benchmark

Benchmark Results

Benchmark Summary

Date: 2026-05-17T10:24:07.618Z
Tool: autocannon (10 connections, 10s duration)
Target: http://localhost:4001

Per-Endpoint Results

Endpoint	Method	p50	p95	p99	Avg RPS	Errors
GET /health вњ…	GET	2.00 ms	4.00 ms	5.00 ms	3В 408	0
POST /api/auth/register вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 939	0
POST /api/auth/login вњ…	POST	2.00 ms	5.00 ms	6.00 ms	3В 026	0
POST /api/auth/refresh вњ…	POST	2.00 ms	7.00 ms	11.00 ms	3В 190	0
GET /api/auth/oauth/google/callback вњ…	GET	2.00 ms	7.00 ms	10.00 ms	3В 203	0
GET /api/users вњ…	GET	2.00 ms	7.00 ms	11.00 ms	3В 178	0
POST /api/users вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 508	0
GET /api/jobs вњ…	GET	2.00 ms	7.00 ms	10.00 ms	3В 195	0
POST /api/jobs вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 480	0
GET /api/proposals вњ…	GET	2.00 ms	7.00 ms	10.00 ms	3В 180	0
POST /api/proposals вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 523	0
POST /api/payments вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 559	0
GET /api/reviews вњ…	GET	2.00 ms	7.00 ms	10.00 ms	3В 181	0
POST /api/reviews вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 523	0
GET /api/messages вњ…	GET	3.00 ms	7.00 ms	10.00 ms	3В 163	0
POST /api/messages вњ…	POST	3.00 ms	5.00 ms	6.00 ms	2В 516	0
GET /api/notifications вњ…	GET	3.00 ms	7.00 ms	11.00 ms	3В 137	0
POST /api/notifications вњ…	POST	4.00 ms	5.00 ms	6.00 ms	2В 395	0
POST /api/uploads вњ…	POST	3.00 ms	8.00 ms	13.00 ms	3В 024	0
GET /api/search вњ…	GET	3.00 ms	8.00 ms	13.00 ms	3В 067	0
GET /api/admin/metrics вњ…	GET	3.00 ms	8.00 ms	12.00 ms	3В 003	0

Thresholds

Metric	Threshold	Status
p99 latency	≤ 500 ms	✅ Pass
Error rate	≤ 1%	✅ Pass
Min RPS	≥ 50	✅ Pass

Environment

• Node.js: v20.18.1
• Platform: win32
• Architecture: x64

Thresholds

Threshold	Value
p99 latency	≤ 500 ms
Error rate	≤ 1%
Min RPS	≥ 50

Closes #30