Add performance regression detection: indexes, timing middleware, benchmark script

Nightshift-Task: perf-regression
Nightshift-Ref: https://github.com/marcus/nightshift

scripts/perf-benchmark.js

@@ -0,0 +1,62 @@
+#!/usr/bin/env node
+'use strict';
+
+const BASE_URL = process.env.BENCHMARK_URL || 'http://localhost:3001';
+const ITERATIONS = 5;
+const MEAN_THRESHOLD_MS = parseInt(process.env.SLOW_THRESHOLD_MS || '500', 10);
+
+const ENDPOINTS = [
+  { label: 'GET /api/paychecks', path: `/api/paychecks?year=${new Date().getFullYear()}&month=${new Date().getMonth() + 1}` },
+  { label: 'GET /api/financing', path: '/api/financing' },
+  { label: 'GET /api/summary/annual', path: `/api/summary/annual?year=${new Date().getFullYear()}` },
+];
+
+async function measureEndpoint(endpoint) {
+  const times = [];
+  for (let i = 0; i < ITERATIONS; i++) {
+    const start = Date.now();
+    const res = await fetch(`${BASE_URL}${endpoint.path}`);
+    const duration = Date.now() - start;
+    if (!res.ok) {
+      console.warn(`  [warn] ${endpoint.label} returned HTTP ${res.status}`);
+    }
+    times.push(duration);
+  }
+  const min = Math.min(...times);
+  const max = Math.max(...times);
+  const mean = Math.round(times.reduce((a, b) => a + b, 0) / times.length);
+  return { min, mean, max };
+}
+
+(async () => {
+  console.log(`Benchmarking ${BASE_URL} (${ITERATIONS} iterations each, threshold ${MEAN_THRESHOLD_MS}ms)\n`);
+
+  let failed = false;
+
+  for (const endpoint of ENDPOINTS) {
+    let stats;
+    try {
+      stats = await measureEndpoint(endpoint);
+    } catch (err) {
+      console.error(`  [error] ${endpoint.label}: ${err.message}`);
+      failed = true;
+      continue;
+    }
+
+    const flag = stats.mean >= MEAN_THRESHOLD_MS ? ' *** SLOW ***' : '';
+    console.log(`${endpoint.label}`);
+    console.log(`  min=${stats.min}ms  mean=${stats.mean}ms  max=${stats.max}ms${flag}`);
+
+    if (stats.mean >= MEAN_THRESHOLD_MS) {
+      failed = true;
+    }
+  }
+
+  console.log('');
+  if (failed) {
+    console.error('FAIL: one or more endpoints exceeded the threshold or errored.');
+    process.exit(1);
+  } else {
+    console.log('PASS: all endpoints within threshold.');
+  }
+})();