feat(load-tests): add K6 load testing suite for critical API paths

K6 scripts for 4 critical paths:
- Auth (100 VU): login, register, profile
- Listings (500 VU): search with filters, detail view
- Search (200 VU): full-text + geo search
- Payments (50 VU): create payment, list transactions

SLA thresholds: p50<200ms, p95<500ms, p99<1s, error<1%.
CI: manual workflow_dispatch with suite selector.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

load-tests/scripts/listings.js

@@ -0,0 +1,116 @@
+import http from 'k6/http';
+import { check, sleep } from 'k6';
+import { Trend } from 'k6/metrics';
+import { BASE_URL, SLA_THRESHOLDS, registerTestUser, authHeaders } from '../lib/config.js';
+
+const searchDuration = new Trend('listings_search_duration', true);
+const detailDuration = new Trend('listings_detail_duration', true);
+
+export const options = {
+  scenarios: {
+    listings_load: {
+      executor: 'ramping-vus',
+      startVUs: 0,
+      stages: [
+        { duration: '30s', target: 100 },
+        { duration: '2m', target: 500 },   // peak: 500 concurrent
+        { duration: '30s', target: 0 },
+      ],
+      gracefulRampDown: '10s',
+    },
+  },
+  thresholds: {
+    ...SLA_THRESHOLDS,
+    listings_search_duration: ['p(95)<500'],
+    listings_detail_duration: ['p(95)<300'],
+  },
+};
+
+export function setup() {
+  // Register a user and create some listings for search/detail tests
+  const tokens = registerTestUser(http);
+  if (!tokens) return { accessToken: null, listingIds: [] };
+
+  const listingIds = [];
+  const cities = ['Hà Nội', 'TP. Hồ Chí Minh', 'Đà Nẵng'];
+  const types = ['APARTMENT', 'HOUSE', 'LAND'];
+
+  for (let i = 0; i < 10; i++) {
+    const listing = {
+      title: `K6 Load Test Listing ${i}`,
+      description: `Performance test listing #${i} for load testing`,
+      transactionType: i % 2 === 0 ? 'SALE' : 'RENT',
+      propertyType: types[i % types.length],
+      address: `${100 + i} Đường Tải Thử`,
+      ward: 'Phường 1',
+      district: 'Quận 1',
+      city: cities[i % cities.length],
+      latitude: 10.7769 + (i * 0.001),
+      longitude: 106.7009 + (i * 0.001),
+      area: 50 + (i * 10),
+      bedrooms: 1 + (i % 4),
+      bathrooms: 1 + (i % 3),
+      floors: 1 + (i % 3),
+      priceVND: 1000000000 + (i * 500000000),
+      direction: 'EAST',
+    };
+
+    const res = http.post(
+      `${BASE_URL}/listings`,
+      JSON.stringify(listing),
+      { headers: authHeaders(tokens.accessToken), tags: { name: 'setup_create_listing' } },
+    );
+
+    if (res.status === 201 || res.status === 200) {
+      try {
+        listingIds.push(JSON.parse(res.body).id);
+      } catch (_) { /* skip */ }
+    }
+  }
+
+  return { accessToken: tokens.accessToken, listingIds };
+}
+
+export default function (data) {
+  const iter = __ITER;
+
+  if (iter % 3 === 0 && data.listingIds.length > 0) {
+    // Detail view — pick a random listing
+    const id = data.listingIds[iter % data.listingIds.length];
+    const res = http.get(`${BASE_URL}/listings/${id}`, {
+      tags: { name: 'GET /listings/:id' },
+    });
+
+    detailDuration.add(res.timings.duration);
+    check(res, {
+      'detail: status 200': (r) => r.status === 200,
+      'detail: has id': (r) => {
+        try { return JSON.parse(r.body).id !== undefined; } catch { return false; }
+      },
+    });
+  } else {
+    // Search listings with various filters
+    const queries = [
+      '?limit=20&offset=0',
+      '?propertyType=APARTMENT&limit=10',
+      '?transactionType=SALE&limit=10',
+      '?city=Hà Nội&limit=10',
+      '?limit=20&offset=20',
+    ];
+    const query = queries[iter % queries.length];
+
+    const res = http.get(`${BASE_URL}/listings${query}`, {
+      tags: { name: 'GET /listings (search)' },
+    });
+
+    searchDuration.add(res.timings.duration);
+    check(res, {
+      'search: status 200': (r) => r.status === 200,
+      'search: has data array': (r) => {
+        try { return Array.isArray(JSON.parse(r.body).data); } catch { return false; }
+      },
+    });
+  }
+
+  sleep(Math.random() * 1 + 0.3);
+}