docs: add comprehensive K6 load testing guide with API structure

- Document all API endpoints (auth, listings, payments, search)
- Include DTOs and request/response body shapes
- Document authentication methods and rate limits
- Provide database and environment configuration
- Include existing test setup (Playwright, Vitest)
- Detail CI/CD pipeline structure
- Recommend K6 endpoints and test patterns
- Provide file location references for quick lookup

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/i18n/request.ts

@@ -0,0 +1,16 @@
+import { getRequestConfig } from 'next-intl/server';
+import { routing } from './routing';
+
+export default getRequestConfig(async ({ requestLocale }) => {
+  let locale = await requestLocale;
+
+  // Ensure a valid locale is used
+  if (!locale || !routing.locales.includes(locale as (typeof routing.locales)[number])) {
+    locale = routing.defaultLocale;
+  }
+
+  return {
+    locale,
+    messages: (await import(`../messages/${locale}.json`)).default,
+  };
+});